The Activity-Regulated Cytoskeleton-associated protein (Arc), also referred to as Arg3.1 (Activity-Regulated Gene), is an immediate-early gene predominantly found in mammals that has been related to synaptic plasticity, learning and memory processes [, , , , ]. It has been shown that Arc/Arg3.1 expression increases with strong synaptic activation []. Its mRNA is transported to activated dendritic regions, conferring on the protein-distribution temporal correlation with the inducing stimulus and spatial specificity [, ].Via interactions with dynamin and endophilin isoforms, the Arc/Arg3.1 protein enhances receptor endocytosis []. Specifically, it modulates trafficking of neuronal AMPA-type glutamate receptors (AMPARs) by accelerating endocytosis and reducing surface expression []. In particular, Arc/Arg3.1 has been shown to reduce the number of GluR2/3 receptors, leading to a decrease in AMPAR-mediated synaptic currents []. These observations are consistent with a role in homeostatic regulation of synaptic strength [, ].
Arc repressor act by the cooperative binding of two Arc repressor dimers to a 21-base-pair operator site. Each Arc dimer uses an antiparallel β-sheet to recognise bases in the major groove [].
This entry represents the C-terminal capsid-like domain of the Activity-regulated cytoskeleton-associated protein (Arc). The Arc protein modulates the trafficking of AMPA-type glutamate receptors [, ]. The tertiary structure of this two-lobe capsid domain is similar to the capsid domain of HIV gag protein. The domain is thought to have evolved from the capsid domain of Ty3/Gypsy retrotransposon [, ].
This entry represents the N-terminal matrix-like (MA) domain of the Activity-Regulated Cytoskeleton-Associated protein (Arc). This domain might be involved in stabilising the relative domain orientations of the capside-like domain (CA) upon capsid assembly []. Arc is a regulator of synaptic scaling and dendrite remodelling [].
The Antirepressor protein ant from Salmonella phage P22 prevents the prophage p22 c2 repressor protein from binding to its operators. It also inhibits the action of other prophage repressor proteins, including those of phages lambda and 434. The synthesis of antirepressor is negatively regulated by the protein products of the two other immi genes, mnt and arc [, , ]. This entry represents the N-terminal domain of this protein and similar proteins from tailed bacteriophages (Caudovirales) and bacterial prophages mostly found in Proteobacteria.
Leucine-rich repeats (LRR, see ) consist of 2-45 motifs of 20-30 amino acids in length that generally folds into an arc or horseshoe shape []. LRRs occur in proteins ranging from viruses to eukaryotes, and appear to provide a structural framework for the formation of protein-protein interactions []. Proteins containing LRRs include tyrosine kinase receptors, cell-adhesion molecules, virulence factors, and extracellular matrix-binding glycoproteins, and are involved in a variety of biological processes, including signal transduction, cell adhesion, DNA repair, recombination, transcription, RNA processing, disease resistance, apoptosis, and the immune response.LRRs are often flanked by cysteine-rich domains: an N-terminal LRR domain () and a C-terminal LRR domain. This entry represents the C-terminal LRR domain.
This superfamily represents domains with a ribbon-helix-helix core topology consisting of four helices in an open array of two hairpins. Such domains are found in several bacterial and phage repressors, including the Escherichia coli methionine repressor (MetJ), which when combined with S-adenosylmethionine (SAM) represses the expression of the methionine regulon and of enzymes involved in SAM synthesis []. Other bacterial and phage repressors containing domains with a similar fold include the bacterial plasmid-encoded repressors CopG (), the bacterial omega transcription repressor [], and the phage repressors Arc []and Mnt []. These repressors are usually obligate dimers, which pair through a single N-terminal strand, and possess a C-terminal helix-turn-helix unit [].
This entry represents the RNA recognition motif 1 (RRM1) of hnRNP A2/B1. Heterogeneous nuclear ribonucleoprotein (hnRNP) A2/B1 is an RNA trafficking response element-binding protein that interacts with the hnRNP A2 response element (A2RE), a cis-acting signal present in certain trafficked mRNAs, including those encoding myelin basic protein (MBP), CaMKII, neurogranin, and Arc [, , ]. Besides RNA trafficking, hnRNP A2/B1 is also involved in many aspectsof mRNA processing, including packaging of nascent transcripts, splicing of pre-mRNAs, and translational regulation []. For instance, it functions as a splicing factor that regulates alternative splicing of tumour suppressors, such as BIN1, WWOX, the antiapoptotic proteins c-FLIP and caspase-9B, the insulin receptor (IR), and the RON proto-oncogene among others []. The overexpression of hnRNP A2/B1 has been linked to many cancers and may play a role in tumor cell differentiation []. hnRNP A2/B1 contains two RNA recognition motifs (RRMs), followed by a long glycine-rich region at the C terminus [].
Heterogeneous nuclear ribonucleoprotein (hnRNP) A2/B1 is an RNA trafficking response element-binding protein that interacts with the hnRNP A2 response element (A2RE), a cis-acting signal present in certain trafficked mRNAs, including those encoding myelin basic protein (MBP), CaMKII, neurogranin, and Arc [, , ]. Besides RNA trafficking, hnRNP A2/B1 is also involved in many aspects of mRNA processing, including packaging of nascent transcripts, splicing of pre-mRNAs, and translational regulation []. For instance, it functions as a splicing factor that regulates alternative splicing of tumour suppressors, such as BIN1, WWOX, the antiapoptotic proteins c-FLIP and caspase-9B, the insulin receptor (IR), and the RON proto-oncogene among others []. The overexpression of hnRNP A2/B1 has been linked to many cancers and may play a role in tumor cell differentiation []. hnRNP A2/B1 contains two RNA recognition motifs (RRMs), followed by a long glycine-rich region at the C terminus [].
This superfamily represents a leucine-rich repeat (LRR), right-handed beta-alpha superhelix domain, such as that found in bacterial invasion protein internalin []or in the L domain from members of the epidermal growth-factor receptor (EGFR) family [].Leucine-rich repeats (LRR) consist of 2-45 motifs of 20-30 amino acids in length that generally folds into an arc or horseshoe shape []. LRRs occur in proteins ranging from viruses to eukaryotes, and appear to provide a structural framework for the formation of protein-protein interactions [, ].Proteins containing LRRs include tyrosine kinase receptors, cell-adhesion molecules, virulence factors, and extracellular matrix-binding glycoproteins, and are involved in a variety of biological processes, including signal transduction, cell adhesion, DNA repair, recombination, transcription, RNA processing, disease resistance, apoptosis, and the immune response [].
In eukaryotes, there are three different forms of DNA-dependent RNA polymerases () transcribing different sets of genes. Each class of RNA polymerase is an assemblage of ten to twelve different polypeptides. In archaebacteria, there is generally a single form of RNA polymerase which also consists of an oligomeric assemblage of 10 to 13 polypeptides. A component of 14 to 18kDa shared by all three forms of eukaryotic RNA polymerases and which has been sequenced in budding yeast (gene RPB6 or RPO26), in Schizosaccharomyces pombe (Fission yeast) (gene rpb6 or rpo15), in human and in African swine fever virus (ASFV) is evolutionary related to the archaebacterial subunit Rpo6 (also known as subunit K). The archaebacterial protein is colinear with the C-terminal part of the eukaryotic subunit. The structures of the omega subunit and RBP6, and the structures of the omega/beta' and RPB6/RPB1 interfaces, suggest a molecular mechanism for the function of omega and RPB6 in promoting RNAP assembly and/or stability. The conserved regions of omega and RPB6 form a compact structural domain that interacts simultaneously with conserved regions of the largest RNAP subunit and with the C-terminal tail following a conserved region of the largest RNAP subunit. The second half of the conserved region of omega and RPB6 forms an arc that projects away from the remainder of the structural domain and wraps over and around the C-terminal tail of the largest RNAP subunit, clamping it in a crevice, and threading the C-terminal tail of the largest RNAP subunit through the narrow gap between omega and RPB6 [].
Growth hormone (GH) is a pituitary hormone involved in cell and overall bodygrowth, carbohydrate-protein-lipid metabolism and osmotic homeostasis.Control of GH release was initially ascribed to 2 pathways: stimulation byhypothalamic GH-releasing hormone (GHRH) and inhibition by somatostatin.More recently, synthetic compounds, termed GH secretagogues (GHS), were shown to stimulate GH release strongly. This effect is elicited by an orphanG protein-coupled receptor (GPCR), subsequently named the GHS receptor(GHS-R). The endogenous ligand for this receptor was purified from rat andhuman stomach and named ghrelin [].The purified cDNA for ghrelin encodes a 117 amino acid prepropeptide. Thefirst 23 amino acid residues form a signal peptide that is cleaved to leaveproghrelin. Residues 24-51 are cleaved to yield active ghrelin, discardingthe C-terminal fragment []. The 28-residue ghrelin peptide that is left is biologically inactive. Esterification with n-octanoic acid at Ser3 is required for biological activity. Ghrelin mRNA is expressed mainly in thestomach in a distinct endocrine cell type in the submucosal layer, known asX/A-like cells. The active peptide is secreted into the bloodstream ratherthan the stomach. Ghrelin responsive cells are found in abundance in a limited area of the hypothalamic arcuate nucleus (ARC), a region involved incontrol of food intake. As well as releasing GH indirectly via its action on the ARC region of the hypothalamus, ghrelin also appears to be able tostimulate GH release via direct action on the pituitary [].A further variant of the ghrelin peptide exists in rat stomach, des-Gln14-ghrelin. This is produced by alternative splicing and does not require theesterification by n-octanoic acid for biological activity. However, its presence in only small quantities in the stomach suggests ghrelin is themajor active form. The ghrelin active peptide and the GHS receptor sharesequence similarity with motilin and the motilin receptor, respectively, suggesting an evolutionary relationship.
In eukaryotes, there are three different forms of DNA-dependent RNA polymerases () transcribing different sets of genes. Each class of RNA polymerase is an assemblage of ten to twelve different polypeptides. In archaebacteria, there is generally a single form of RNA polymerase which also consists of an oligomeric assemblage of 10 to 13 polypeptides. A component of 14 to 18kDa shared by all three forms of eukaryotic RNA polymerases and which has been sequenced in budding yeast (gene RPB6 or RPO26), in Schizosaccharomyces pombe (Fission yeast) (gene rpb6 or rpo15), in human and in African swine fever virus (ASFV) is evolutionary related to the archaebacterial subunit Rpo6 (also known as subunit K). The archaebacterial protein is colinear with the C-terminal part of the eukaryotic subunit. The structures of the omega subunit and RBP6, and the structures of the omega/beta' and RPB6/RPB1 interfaces, suggest a molecular mechanism for the function of omega and RPB6 in promoting RNAP assembly and/or stability. The conserved regions of omega and RPB6 form a compact structural domain that interacts simultaneously with conserved regions of the largest RNAP subunit and with the C-terminal tail following a conserved region of the largest RNAP subunit. The second half of the conserved region of omega and RPB6 forms an arc that projects away from the remainder of the structural domain and wraps over and around the C-terminal tail of the largest RNAP subunit, clamping it in a crevice, and threading the C-terminal tail of the largest RNAP subunit through the narrow gap between omega and RPB6 [].
Leucine-rich repeats (LRR) consist of 2-45 motifs of 20-30 amino acids in length that generally folds into an arc or horseshoe shape []. LRRs occur in proteins ranging from viruses to eukaryotes, and appear to provide a structural framework for the formation of protein-protein interactions [, ].Proteins containing LRRs include tyrosine kinase receptors, cell-adhesion molecules, virulence factors, and extracellular matrix-binding glycoproteins, and are involved in a variety of biological processes, including signal transduction, cell adhesion, DNA repair, recombination, transcription, RNA processing, disease resistance, apoptosis, and the immune response [, ].Sequence analyses of LRR proteins suggested the existence of several different subfamilies of LRRs. The significance of this classification is that repeats from different subfamilies never occur simultaneously and have most probably evolved independently. It is, however, now clear that all major classes of LRR have curved horseshoe structures with a parallel beta sheet on the concave side and mostly helical elements on the convex side. At least six families of LRR proteins, characterised by different lengths and consensus sequences of the repeats, have been identified. Eleven-residue segments of the LRRs (LxxLxLxxN/CxL), corresponding to the β-strand and adjacent loop regions, are conserved in LRR proteins, whereas the remaining parts of the repeats (herein termed variable) may be very different. Despite the differences, each of the variable parts contains two half-turns at both ends and a "linear"segment (as the chain follows a linear path overall), usually formed by a helix, in the middle. The concave face and the adjacent loops are the most common protein interaction surfaces on LRR proteins. 3D structure of some LRR proteins-ligand complexes show that the concave surface of LRR domain is ideal for interaction with α-helix, thus supporting earlier conclusions that the elongated and curved LRR structure provides an outstanding framework for achieving diverse protein-protein interactions []. Molecular modeling suggests that the conserved pattern LxxLxL, which is shorter than the previously proposed LxxLxLxxN/CxL is sufficient to impart the characteristic horseshoe curvature to proteins with 20- to 30-residue repeats [].
Leucine-rich repeats (LRR) consist of 2-45 motifs of 20-30 amino acids in length that generally folds into an arc or horseshoe shape []. LRRs occur in proteins ranging from viruses to eukaryotes, and appear to provide a structural framework for the formation of protein-protein interactions [, ].Proteins containing LRRs include tyrosine kinase receptors, cell-adhesion molecules, virulence factors, and extracellular matrix-binding glycoproteins, and are involved in a variety of biological processes, including signal transduction, cell adhesion, DNA repair, recombination, transcription, RNA processing, disease resistance, apoptosis, and the immune response [, ].Sequence analyses of LRR proteins suggested the existence of several different subfamilies of LRRs. The significance of this classification is that repeats from different subfamilies never occur simultaneously and have most probably evolved independently. It is, however, now clear that all major classes of LRR have curved horseshoe structures with a parallel beta sheet on the concave side and mostly helical elements on the convex side. At least six families of LRR proteins, characterised by different lengths and consensus sequences of the repeats, have been identified. Eleven-residue segments of the LRRs (LxxLxLxxN/CxL), corresponding to the β-strand and adjacent loop regions, are conserved in LRR proteins, whereas the remaining parts of the repeats (herein termed variable) may be very different. Despite the differences, each of the variable parts contains two half-turns at both ends and a "linear"segment (as the chain follows a linear path overall), usually formed by a helix, in the middle. The concave face and the adjacent loops are the most common protein interaction surfaces on LRR proteins. 3D structure of some LRR proteins-ligand complexes show that the concave surface of LRR domain is ideal for interaction with α-helix, thus supporting earlier conclusions that the elongated and curved LRR structure provides an outstanding framework for achieving diverse protein-protein interactions []. Molecular modeling suggests that the conserved pattern LxxLxL, which is shorter than the previously proposed LxxLxLxxN/CxL is sufficient to impart the characteristic horseshoe curvature to proteins with 20- to 30-residue repeats []. This is a cysteine-containing, leucine-rich repeat which is wide spread amongsteukaryotes proteins but does not appear to be found in archae, bacteria or viruses.
Leucine-rich repeats (LRR) consist of 2-45 motifs of 20-30 amino acids in length that generally folds into an arc or horseshoe shape []. LRRs occur in proteins ranging from viruses to eukaryotes, and appear to provide a structural framework for the formation of protein-protein interactions [, ].Proteins containing LRRs include tyrosine kinase receptors, cell-adhesion molecules, virulence factors, and extracellular matrix-binding glycoproteins, and are involved in a variety of biological processes, including signal transduction, cell adhesion, DNA repair, recombination, transcription, RNA processing, disease resistance, apoptosis, and the immune response [, ].Sequence analyses of LRR proteins suggested the existence of several different subfamilies of LRRs. The significance of this classification is that repeats from different subfamilies never occur simultaneously and have most probably evolved independently. It is, however, now clear that all major classes of LRR have curved horseshoe structures with a parallel beta sheet on the concave side and mostly helical elements on the convex side. At least six families of LRR proteins, characterised by different lengths and consensus sequences of the repeats, have been identified. Eleven-residue segments of the LRRs (LxxLxLxxN/CxL), corresponding to the β-strand and adjacent loop regions, are conserved in LRR proteins, whereas the remaining parts of the repeats (herein termed variable) may be very different. Despite the differences, each of the variable parts contains two half-turns at both ends and a "linear"segment (as the chain follows a linear path overall), usually formed by a helix, in the middle. The concave face and the adjacent loops are the most common protein interaction surfaces on LRR proteins. 3D structure of some LRR proteins-ligand complexes show that the concave surface of LRR domain is ideal for interaction with α-helix, thus supporting earlier conclusions that the elongated and curved LRR structure provides an outstanding framework for achieving diverse protein-protein interactions []. Molecular modeling suggests that the conserved pattern LxxLxL, which is shorter than the previously proposed LxxLxLxxN/CxL is sufficient to impart the characteristic horseshoe curvature to proteins with 20- to 30-residue repeats []. This signature describes a leucine-rich repeat variant (LRV), which has a novel repetitive structural motif consisting of alternating alpha- and 3(10)-helices arranged in a right-handed superhelix, with the absence of the β-sheets present in other LRRs [].
Leucine-rich repeats (LRR) consist of 2-45 motifs of 20-30 amino acids in length that generally folds into an arc or horseshoe shape []. LRRs occur in proteins ranging from viruses to eukaryotes, and appear to provide a structural framework for the formation of protein-protein interactions [, ].Proteins containing LRRs include tyrosine kinase receptors, cell-adhesion molecules, virulence factors, and extracellular matrix-binding glycoproteins, and are involved in a variety of biological processes, including signal transduction, cell adhesion, DNA repair, recombination, transcription, RNA processing, disease resistance, apoptosis, and the immune response [, ].Sequence analyses of LRR proteins suggested the existence of several different subfamilies of LRRs. The significance of this classification is that repeats from different subfamilies never occur simultaneously and have most probably evolved independently. It is, however, now clear that all major classes of LRR have curved horseshoe structures with a parallel beta sheet on the concave side and mostly helical elements on the convex side. At least six families of LRR proteins, characterised by different lengths and consensus sequences of the repeats, have been identified. Eleven-residue segments of the LRRs (LxxLxLxxN/CxL), corresponding to the β-strand and adjacent loop regions, are conserved in LRR proteins, whereas the remaining parts of the repeats (herein termed variable) may be very different. Despite the differences, each of the variable parts contains two half-turns at both ends and a "linear"segment (as the chain follows a linear path overall), usually formed by a helix, in the middle. The concave face and the adjacent loops are the most common protein interaction surfaces on LRR proteins. 3D structure of some LRR proteins-ligand complexes show that the concave surface of LRR domain is ideal for interaction with α-helix, thus supporting earlier conclusions that the elongated and curved LRR structure provides an outstanding framework for achieving diverse protein-protein interactions []. Molecular modeling suggests that the conserved pattern LxxLxL, which is shorter than the previously proposed LxxLxLxxN/CxL is sufficient to impart the characteristic horseshoe curvature to proteins with 20- to 30-residue repeats []. LRRs are often flanked by cysteine-rich domains: an N-terminal LRR domain and a C-terminal LRR domain (). This entry represents the N-terminal LRR domain.
Leucine-rich repeats (LRR) consist of 2-45 motifs of 20-30 amino acids in length that generally folds into an arc or horseshoe shape []. LRRs occur in proteins ranging from viruses to eukaryotes, and appear to provide a structural framework for the formation of protein-protein interactions [, ].Proteins containing LRRs include tyrosine kinase receptors, cell-adhesion molecules, virulence factors, and extracellular matrix-binding glycoproteins, and are involved in a variety of biological processes, including signal transduction, cell adhesion, DNA repair, recombination, transcription, RNA processing, disease resistance, apoptosis, and the immune response [, ].Sequence analyses of LRR proteins suggested the existence of several different subfamilies of LRRs. The significance of this classification is that repeats from different subfamilies never occur simultaneously and have most probably evolved independently. It is, however, now clear that all major classes of LRR have curved horseshoe structures with a parallel beta sheet on the concave side and mostly helical elements on the convex side. At least six families of LRR proteins, characterised by different lengths and consensus sequences of the repeats, have been identified. Eleven-residue segments of the LRRs (LxxLxLxxN/CxL), corresponding to the β-strand and adjacent loop regions, are conserved in LRR proteins, whereas the remaining parts of the repeats (herein termed variable) may be very different. Despite the differences, each of the variable parts contains two half-turns at both ends and a "linear"segment (as the chain follows a linear path overall), usually formed by a helix, in the middle. The concave face and the adjacent loops are the most common protein interaction surfaces on LRR proteins. 3D structure of some LRR proteins-ligand complexes show that the concave surface of LRR domain is ideal for interaction with α-helix, thus supporting earlier conclusions that the elongated and curved LRR structure provides an outstanding framework for achieving diverse protein-protein interactions []. Molecular modeling suggests that the conserved pattern LxxLxL, which is shorter than the previously proposed LxxLxLxxN/CxL is sufficient to impart the characteristic horseshoe curvature to proteins with 20- to 30-residue repeats []. This entry represents a most populated subfamily of leucine-rich repeats.
Leucine-rich repeats (LRR) consist of 2-45 motifs of 20-30 amino acids in length that generally folds into an arc or horseshoe shape []. LRRs occur in proteins ranging from viruses to eukaryotes, and appear to provide a structural framework for the formation of protein-protein interactions [, ].Proteins containing LRRs include tyrosine kinase receptors, cell-adhesion molecules, virulence factors, and extracellular matrix-binding glycoproteins, and are involved in a variety of biological processes, including signal transduction, cell adhesion, DNA repair, recombination, transcription, RNA processing, disease resistance, apoptosis, and the immune response [, ].Sequence analyses of LRR proteins suggested the existence of several different subfamilies of LRRs. The significance of this classification is that repeats from different subfamilies never occur simultaneously and have most probably evolved independently. It is, however, now clear that all major classes of LRR have curved horseshoe structures with aparallel beta sheet on the concave side and mostly helical elements on the convex side. At least six families of LRR proteins, characterised by different lengths and consensus sequences of the repeats, have been identified. Eleven-residue segments of the LRRs (LxxLxLxxN/CxL), corresponding to the β-strand and adjacent loop regions, are conserved in LRR proteins, whereas the remaining parts of the repeats (herein termed variable) may be very different. Despite the differences, each of the variable parts contains two half-turns at both ends and a "linear"segment (as the chain follows a linear path overall), usually formed by a helix, in the middle. The concave face and the adjacent loops are the most common protein interaction surfaces on LRR proteins. 3D structure of some LRR proteins-ligand complexes show that the concave surface of LRR domain is ideal for interaction with α-helix, thus supporting earlier conclusions that the elongated and curved LRR structure provides an outstanding framework for achieving diverse protein-protein interactions []. Molecular modeling suggests that the conserved pattern LxxLxL, which is shorter than the previously proposed LxxLxLxxN/CxL is sufficient to impart the characteristic horseshoe curvature to proteins with 20- to 30-residue repeats []. This domain is often found at the N terminus of tandem leucine rich repeats, mainly in plant proteins.
Leucine-rich repeats (LRR) consist of 2-45 motifs of 20-30 amino acids in length that generally folds into an arc or horseshoe shape []. LRRs occur in proteins ranging from viruses to eukaryotes, and appear to provide a structural framework for the formation of protein-protein interactions [, ].Proteins containing LRRs include tyrosine kinase receptors, cell-adhesion molecules, virulence factors, and extracellular matrix-binding glycoproteins, and are involved in a variety of biological processes, including signal transduction, cell adhesion, DNA repair, recombination, transcription, RNA processing, disease resistance, apoptosis, and the immune response [, ].Sequence analyses of LRR proteins suggested the existence of several different subfamilies of LRRs. The significance of this classification is that repeats from different subfamilies never occur simultaneously and have most probably evolved independently. It is, however, now clear that all major classes of LRR have curved horseshoe structures with a parallel beta sheet on the concave side and mostly helical elements on the convex side. At least six families of LRR proteins, characterised by different lengths and consensus sequences of the repeats, have been identified. Eleven-residue segments of the LRRs (LxxLxLxxN/CxL), corresponding to the β-strand and adjacent loop regions, are conserved in LRR proteins, whereas the remaining parts of the repeats (herein termed variable) may be very different. Despite the differences, each of the variable parts contains two half-turns at both ends and a "linear"segment (as the chain follows a linear path overall), usually formed by a helix, in the middle. The concave face and the adjacent loops are the most common protein interaction surfaces on LRR proteins. 3D structure of some LRR proteins-ligand complexes show that the concave surface of LRR domain is ideal for interaction with α-helix, thus supporting earlier conclusions that the elongated and curved LRR structure provides an outstanding framework for achieving diverse protein-protein interactions []. Molecular modeling suggests that the conserved pattern LxxLxL, which is shorter than the previously proposed LxxLxLxxN/CxL is sufficient to impart the characteristic horseshoe curvature to proteins with 20- to 30-residue repeats []. This entry includes some LRRs that fail to be detected by [, ].
Leucine-rich repeats (LRR) consist of 2-45 motifs of 20-30 amino acids in length that generally folds into an arc or horseshoe shape []. LRRs occur in proteins ranging from viruses to eukaryotes, and appear to provide a structural framework for the formation of protein-protein interactions [, ].Proteins containing LRRs include tyrosine kinase receptors, cell-adhesion molecules, virulence factors, and extracellular matrix-binding glycoproteins, and are involved in a variety of biological processes, including signal transduction, cell adhesion, DNA repair, recombination, transcription, RNA processing, disease resistance, apoptosis, and the immune response [, ].Sequence analyses of LRR proteins suggested the existence of several different subfamilies of LRRs. The significance of this classification is that repeats from different subfamilies never occur simultaneously and have most probably evolved independently. It is, however, now clear that all major classes of LRR have curved horseshoe structures with a parallel beta sheet on the concave side and mostly helical elements on the convex side. At least six families of LRR proteins, characterised by different lengths and consensus sequences of the repeats, have been identified. Eleven-residue segments of the LRRs (LxxLxLxxN/CxL), corresponding to the β-strand and adjacent loop regions, are conserved in LRR proteins, whereas the remaining parts of the repeats (herein termed variable) may be very different. Despite the differences, each of the variable parts contains two half-turns at both ends and a "linear"segment (as the chain follows a linear path overall), usually formed by a helix, in the middle. The concave face and the adjacent loops are the most common protein interaction surfaces on LRR proteins. 3D structure of some LRR proteins-ligand complexes show that the concave surface of LRR domain is ideal for interaction with α-helix, thus supporting earlier conclusions that the elongated and curved LRR structure provides an outstanding framework for achieving diverse protein-protein interactions []. Molecular modeling suggests that the conserved pattern LxxLxL, which is shorter than the previously proposed LxxLxLxxN/CxL is sufficient to impart the characteristic horseshoe curvature to proteins with 20- to 30-residue repeats []. This entry includes some LRRs that fail to be detected by the model.
Leucine-rich repeats (LRR) consist of 2-45 motifs of 20-30 amino acids in length that generally folds into an arc or horseshoe shape []. LRRs occur in proteins ranging from viruses to eukaryotes, and appear to provide a structural framework for the formation of protein-protein interactions [, ].Proteins containing LRRs include tyrosine kinase receptors, cell-adhesion molecules, virulence factors, and extracellular matrix-binding glycoproteins, and are involved in a variety of biological processes, including signal transduction, cell adhesion, DNA repair, recombination, transcription, RNA processing, disease resistance, apoptosis, and the immune response [, ].Sequence analyses of LRR proteins suggested the existence of several different subfamilies of LRRs. The significance of this classification is that repeats from different subfamilies never occur simultaneously and have most probably evolved independently. It is, however, now clear that all major classes of LRR have curved horseshoe structures with a parallel beta sheet on the concave side and mostly helical elements on the convex side. At least six families of LRR proteins, characterised by different lengths and consensus sequences of the repeats, have been identified. Eleven-residue segments of the LRRs (LxxLxLxxN/CxL), corresponding to the β-strand and adjacent loop regions, are conserved in LRR proteins, whereas the remaining parts of the repeats (herein termed variable) may be very different. Despite the differences, each of the variable parts contains two half-turns at both ends and a "linear"segment (as the chain follows a linear path overall), usually formed by a helix, in the middle. The concave face and the adjacent loops are the most common protein interaction surfaces on LRR proteins. 3D structure of some LRR proteins-ligand complexes show that the concave surface of LRR domain is ideal for interaction with α-helix, thus supporting earlier conclusions that the elongated and curved LRR structure provides an outstanding framework for achieving diverse protein-protein interactions []. Molecular modeling suggests that the conserved pattern LxxLxL, which is shorter than the previously proposed LxxLxLxxN/CxL is sufficient to impart the characteristic horseshoe curvature to proteins with 20- to 30-residue repeats []. These are small, all beta strand domains, structurally described for the protein Internalin (InlA) and related proteins InlB, InlC, InlH from the pathogenic bacterium Listeria monocytogenes. Their function appears to be mainly structural: They are fused to the C-terminal end of leucine-rich repeats (LRR), significantly stabilising the LRR, and forming a common rigid entity with the LRR. They are themselves not involved in protein-protein-interactions but help to present the adjacent LRR-domain for this purpose. These domains belong to the family of Ig-like domains in that they consist of two sandwiched beta sheets that follow the classical connectivity of Ig-domains. The beta strands in one of the sheets is, however, much smaller than in most standard Ig-like domains, making it somewhat of an outlier [, , , ].
