SHD (SH2 domain-containing adapter protein D) is thought to act as an adapter protein in the central nervous system. SHD contains five YXXP motifs, a substrate sequence preferred by Abl tyrosine kinases, in addition to a proline-rich region and a C-terminal SH2 domain [].
This entry represents the SH2 domain of SHD.SHD (SH2 domain-containing adapter protein D) is thought to act as an adapter protein in the central nervous system. SHD contains five YXXP motifs, a substrate sequence preferred by Abl tyrosine kinases, in addition to a proline-rich region and a C-terminal SH2 domain [].
Human stonins, like their Drosophila homologue stoned B, are supposed to beendocytotic proteins involved in clathrin-mediated endocytosis at synapses.The two human stonins, as well as their Drosophila melanogaster (Fruit fly) and Caenorhabditis elegans homologues, exhibit a modular structure consisting ofan N-terminal proline- and serine-rich domain, a central stonin homologydomain (SHD), and a C-terminal domain homologous to the signal-binding domainof the mu subunits of adaptor protein (AP) complexes (mu-homology domain). The ~140 amino-acid SHD domain has not been described in other proteins and may thus be unique to members of the stonin family. Its function is not yet known [, ].
Synaptotagmin-like proteins (Slps) contain a N-terminal RabBD (Rab-binding) domain and two C-terminal C2 domains, C2A and C2B []. The characteristic feature of the Slp family is the N-terminal domain (referred to as SHD for Slp Homology Domain), which is not found in other C-type tandem C2 proteins []. SHD functions as a specific Rab27A/B-binding domain []. This entry represents the C2B domain. The C2 domain is a Ca2+-dependent membrane-targeting module found in many cellular proteins involved in signal transduction or membrane trafficking. C2 domains are unique among membrane targeting domains in that they show wide range of lipid selectivity for the major components of cell membranes, including phosphatidylserine and phosphatidylcholine. This C2 domain is about 116 amino-acid residues and is located between the two copies of the C1 domain in Protein Kinase C and the protein kinase catalytic domain []. Regions with significant homology []to the C2-domain have been found in many proteins. The C2 domain is thought to be involved in calcium-dependent phospholipid binding []and in membrane targetting processes such as subcellular localisation. The 3D structure of the C2 domain of synaptotagmin has been reported[], the domain forms an eight-stranded β-sandwich constructed around a conserved 4-stranded motif, designated a C2 key []. Calcium binds in a cup-shaped depression formed by the N- and C-terminal loops of the C2-key motif. Structural analyses of several C2 domains have shown them to consist of similar ternary structures in which three Ca2+-binding loops are located at the end of an 8 stranded antiparallel β-sandwich.
Synaptotagmin-like proteins (Slps) contain a N-terminal RabBD (Rab-binding) domain and two C-terminal C2 domains, C2A and C2B []. The characteristic feature of the Slp family is the N-terminal domain (referred to as SHD for Slp Homology Domain), which is not found in other C-type tandem C2 proteins []. SHD functions as a specific Rab27A/B-binding domain []. The C2B domain of Slp4 (also known as Granuphilin) interact with the plasma membrane lipid phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P2][]. C2 domains fold into an 8-standed β-sandwich that can adopt 2 structural arrangements, type I and type II, distinguished by a circular permutation involving their N- and C-terminal beta strands. Many C2 domains are Ca2+-dependent membrane-targeting modules that bind a wide variety of substances including phospholipids, inositol polyphosphates, and intracellular proteins. Most C2 domain proteins are either signal transduction enzymes that contain a single C2 domain, such as protein kinase C, or membrane trafficking proteins which contain at least two C2 domains, such as synaptotagmin 1. However, there are a few exceptions to this including RIM isoforms and some splice variants of piccolo/aczonin andintersectin which only have a single C2 domain. C2 domains with a calcium binding region have negatively charged residues, primarily aspartates, that serve as ligands for calcium ions [, , , , , , , ].
Synaptotagmin-like protein 4 (SYTL4, Slp4), also known as granuphilin or exophilin-2, belongs to the synaptotagmin-like protein family (Slp), which is a group of putative membrane trafficking proteins []. The characteristic feature of the Slp family is the N-terminal Slp homology domain (SHD), which functions as a Rab27-binding domain and C-terminal tandem C2 domains (known as the C2A domain and C2B domain), putative Ca2+-binding motifs [, ]. SHD consists of two conserved regions, designated SHD1 and SHD2, which may function as protein interaction sites. The SHD1 and SHD2 of Slp4 are separated by a putative FYVE zinc finger, which resembles a FYVE-related domain that is structurally similar to the canonical FYVE domains but lacks the three signature sequences: an N-terminal WxxD motif (x for any residue), the central basic R(R/K)HHCRxCG patch, and a C-terminal RVC motif.There are several alternatively spliced isoform of Slp4. Slp4-a (granuphilin-a) has two C2 domains, whereas Slp4-b (granuphilin-b) contains only the first C2 domain. Expression of Slp4-a inhibits regulated secretion in endocrine cells. Slp4-a binds to both the GTP- and GDP-bound forms of Rab27A and inhibits a specific GTP/GDP exchange cycle required for dense-core vesicle exocytosis []. Slp4 has been detected in the pancreatic islet, in particular in insulin-positive beta cells, and in pituitary []. This entry represents the FYVE-related domain of synaptotagmin-like protein 4.
Synaptotagmin-like protein 4 (SYTL4, Slp4), also known as granuphilin or exophilin-2, belongs to the synaptotagmin-like protein family (Slp), which is a group of putative membrane trafficking proteins []. The characteristic feature of the Slp family is the N-terminal Slp homology domain (SHD), which functions as a Rab27-binding domain and C-terminal tandem C2 domains (known as the C2A domain and C2B domain), putative Ca2+-binding motifs [, ]. SHD consists of two conserved regions, designated SHD1 and SHD2, which may function as protein interaction sites. The SHD1 and SHD2 of Slp4 are separated by a putative FYVE zinc finger, which resembles a FYVE-related domain that is structurally similar to the canonical FYVE domains but lacks the three signature sequences: an N-terminal WxxD motif (x for any residue), the central basic R(R/K)HHCRxCG patch, and a C-terminal RVC motif.There are several alternatively spliced isoform of Slp4. Slp4-a (granuphilin-a) has two C2 domains, whereas Slp4-b (granuphilin-b) contains only the first C2 domain. Expression of Slp4-a inhibits regulated secretion in endocrine cells. Slp4-a binds to both the GTP- and GDP-bound forms of Rab27A and inhibits a specific GTP/GDP exchange cycle required for dense-core vesicle exocytosis []. Slp4 has been detected inthe pancreatic islet, in particular in insulin-positive beta cells, and in pituitary [].
Melanophilin, also termed SlaC2-a, or exophilin-3, is a GTP-bound form of Rab27A-, myosin Va-, and actin-binding protein present on melanosomes. It is involved in the control of transferring of melanosomes from microtubules to actin filaments. It also functions as a melanocyte type myosin Va (McM5) binding partner and directly activates the actin-activated ATPase activity of McM5 through forming a tripartite protein complex with Rab27A and an actin-based motor myosin Va [,]. SlaC2-a belongs to the Slp homologue lacking C2 domains (Slac2) family. It contains an N-terminal Slp homology domain (SHD), but lacks tandem C2 domains. The SHD consists of two conserved regions, designated SHD1 (Slp homology domain 1) and SHD2, which may function as protein interaction sites []. The SHD1 and SHD2 of SlaC2-a are separated by a putative FYVE zinc finger, which resembles a FYVE-related domain that is structurally similar to the canonical FYVE domains but lacks the three signature sequences: an N-terminal WxxD motif (x for any residue), the central basic R(R/K)HHCRxCG patch, and a C-terminal RVC motif. Moreover, Slac2-a has a middle myosin-binding domain and a C-terminal actin-binding domain [].
