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Search results 1 to 8 out of 8 for C4b

Category restricted to ProteinDomain (x)

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Categories

Category: ProteinDomain
Type Details Score
Protein Domain
Type: Family
Description: This entry represents complement component C4-A. C4-A is proteolytically processed to generate subcomponents C4a and C4b by complement component activated C1s (classical pathway) []or mannan-binding lectin-associated serine peptidases (lectin pathway) [, ]. C4a is an anaphylatoxin, whereas C4b forms a complex with complement subcomponent C2a to form the C3/C5 convertase, which is stabilized by Mg2+[, ]. The C3/C5 convertase has trypsin-like specificity [].
Protein Domain
Type: Family
Description: This entry represents a group of membrane cofactor proteins (also known as CD46 or TLX). Human CD46 acts as a cofactor for complement factor I, a serine protease which protects autologous cells against complement-mediated injury by cleaving C3b and C4b deposited on host tissue []. Rat CD46 may be involved in the fusion of the spermatozoa with the oocyte during fertilization [].
Protein Domain
Type: Family
Description: This entry represents complement component C2, a component of the classical and lectin activation pathway of complement. C2 is cleaved by C1s (classical) or mannan-binding lectin-associated serine peptidases (lectin) into C2a and C2b []. C2a is a serine endopeptidase from family S1 (chymotrypsin family; MEROPS identifier S01.194) which complexes with C4b to form the C3/C5 convertase []. The complex is stabilized by Mg2+[, ]. The C3/C5 convertase has trypsin-like specificity []. C2 deficiency is the commonest human complement deficiency, which can result in systemic lupus erythematosus-like immune complex diseases []. The C2 gene is part of the major histocompatabaility complex [].
Protein Domain
Type: Family
Description: This group represents complement control proteins, vaccinia virus C3-type. The vaccinia virus complement control protein C3 is involved in modulating the host inflammatory response by blocking both classical and alternative pathways of complement activity through its ability to bind host complement components C3b and C4b (complement 3b and 4b, respectively) []. Protein B5, another member of this group, binds complement components C3 and C1q []. By blocking complement activation at multiple sites, the complement control proteins can down-regulate pro-inflammatory chemotactic factors (C3a, C4a, and C5a), resulting in reduced cellular influx and inflammation..
Protein Domain
Type: Domain
Description: The extracellular sushi domain is characterised by a consensus sequence spanning ~60 residues containing four invariant cysteine residues forming two disulfide-bridges (I-III and II-IV), a highly conserved tryptophan, and conserved glycine, proline, and hydrophobic residues []. Sushi domains are known to be involved in many recognition processes, including the binding of several complement factors to fragments C3b and C4b []. The sushi domain is also known as the complement control protein (CCP) module or the short consensus repeat (SCR). Several structure of the sushi domain have been solved (see for example ) []. The sushi domain folds into a small and compact hydrophobic core enveloped by six β-strands and stabilised by two disulfide bridges. The relative structural orientation of the β-2 and β-4 strands is shared by all the sushi structures, whereas the topology of the other strands relative to this central conserved core is variable, especially at the regions that form the interfaces with the preceding and following domains [].
Protein Domain
Type: Domain
Description: This domain is found in complement component proteins, complement component factor 1 and agrin. Complement components C5b, C6, C7 C8 and C9 are the constituents of the membrane attack complex (MAC) that plays a key role in the innate and adaptive immune response by forming pores in the plasma membrane of target cells. Its assembly is initiated by protelytic cleavage of C5 into C5a and C5b. C5b binds sequentially C6, C7, C8 and multiple copies of the pore-forming subunit C9. Factor I is responsible for cleaving alpha chains of C4B and C3B in the presence of the cofactors C4-binding protein and factor H respectively. Agrin is a component of the basal lamina that causes the aggregation of acetylcholine receptors and acetylcholine-esterase on the surface of muscle fibres of the neuromuscular junction.
Protein Domain
Type: Homologous_superfamily
Description: The extracellular sushi domain is characterised by a consensus sequence spanning ~60 residues containing four invariant cysteine residues forming two disulfide-bridges (I-III and II-IV), a highly conserved tryptophan, and conserved glycine, proline, and hydrophobic residues []. Sushi domains are known to be involved in many recognition processes, including the binding of several complement factors to fragments C3b and C4b []. The sushi domain is also known as the complement control protein (CCP) module or the short consensus repeat (SCR). Several structure of the sushi domain have been solved (see for example ) []. The sushi domain folds into a small and compact hydrophobic core enveloped by six β-strands and stabilised by two disulfide bridges. The relative structural orientation of the β-2 and β-4 strands is shared by all the sushi structures, whereas the topology of the other strands relative to this central conserved core is variable, especially at the regions that form the interfaces with the preceding and following domains [].
Protein Domain
Type: Conserved_site
Description: Low-density lipoprotein (LDL) receptors are the major cholesterol-carrying lipoproteins of plasma. Seven successive cysteine-rich repeats of about 40 amino acids are present in the N-terminal of this multidomain membrane protein []. Similar domains have been found (see references in []) in other extracellular and membrane proteins which are listed below: Vertebrate very low density lipoprotein (VLDL) receptor, which binds and transports VLDL. Its extracellular domain is composed of 8 LDLRA domains, 3 EGF-like domains and 6 LDL-receptor class B domains (LDLRB). Vertebrate low-density lipoprotein receptor-related protein 1 (LRP1) (reviewed in []), which may act as a receptor for the endocytosis of extracellular ligands. LRP1 contains 31 LDLRA domains and 22 EGF-like domains. Vertebrate low-density lipoprotein receptor-related protein 2 (LRP2) (also known as gp330 or megalin). LRP2 contains 36 LDLRA domains and 17 EGF-like domains. A LRP-homologue from Caenorhabditis elegans, which contains 35 LDLRA domains and 17 EGF-like domains. Drosophila putative vitellogenin receptor, with 13 copies of LDLRA domains and 17 EGF-like repeats. Complement factor I, which is responsible for cleaving the alpha-chains of C4b and C3b. It consists of a FIMAC domain (Factor I/MAC proteins C6/C7), a scavenger receptor-like domain, 2 copies of LDLRA and a C-terminal serine protease domain. Complement components C6, C7, C8 and C9. They contain each one LDLRA domain. Perlecan, a large multidomain basement membrane heparan sulphate proteoglycan composed of 4 LDLRA domains, 3 LamB domains, 12 laminin EGF- like domains, 14-21 IG-like domains, 3 LamG domains, and 4 EGF-like domains. A similar but shorter proteoglycan (UNC52) is found in Caenorhabditis elegans which has 3 repeats of LDLRA. Invertebrate giant extracellular hemoglobin linker chains, which allow heme-containing chains to construct giant hemoglobin (1 LDLRA domain). G-protein coupled receptor Grl101 of the snail Lymnaea stagnalis, which might directly transduce signals carried by large extracellular proteins. Vertebrate enterokinase (EC 3.4.21.9), a type II membrane protein of the intestinal brush border, which activates trypsinogen. It consists at least of a catalytic light chain and a multidomain heavy chain which has 2 LDLRA, a MAM domain (see ), a SRCR domain (see ) and a CUB domain (see ).Human autosomal dominant polycystic kidney disease protein 1 (PKD1), which is involved in adhesive protein-protein and protein-carbohydrate interactions. The potential calcium-binding site of its single LDLRA domain is missing. Vertebrate integral membrane protein DGCR2/IDD, a potential adhesion receptor with 1 LDLRA domain, a C-type lectin and a VWFC domain (see ).Drosophila serine protease nudel (EC 3.4.21.-), which is involved in the induction of dorsoventral polarity of the embryo. It has 11 LDLRA domains, 3 of which miss the first disulphide bond (C1-C3). Avian subgroup A rous sarcoma virus receptor (1 copy of LDLRA). Bovine Sco-spondin, which is secreted by the subcommissural organ in embryos and is involved in the modulation of neuronal aggregation. It contains at least 2 EGF-like domains and 3 LDLRA domains. The LDL-receptor class A domain contains 6 disulphide-bound cysteines []and a highly conserved cluster of negatively charged amino acids, of which many are clustered on one face of the module []. A schematic representation of this domain is shown here: +---------------------+ +--------------------------------+| | | |-CxxxxxxxxxxxxCxxxxxxxxCxxxxxxxxCxxxxxxxxxxCxxxxxxxxxxxxxxxxxxxxxC-|*******************************************| |+----------------------------+'C': conserved cysteine involved in a disulphide bond.'x': any residue.'*': position of the pattern.In LDL-receptors the class A domains form the binding site for LDL []and calcium. The acidic residues between the fourth and sixth cysteines are important for high-affinity binding of positively charged sequences in LDLR's ligands []. The repeat has been shown []to consist of a β-hairpin structure followed by a series of β-turns. The binding of calcium seems to induce no significant conformational change.