| Primary Identifier | IPR037749 | Type | Domain |
| Short Name | Ext_Synaptotagmin_C2B |
| description | The extended-synaptotagmins derive their name from their partial domain structure similarity to the synaptotagmins, characterised by an N-terminal membrane anchor and cytosolically exposed C2 domains. Additionally they contain an SMP (synaptotagmin-like mitochondrial-lipid-binding protein) domain and multiple C2 domains (five in E-Syt1 and three in E-Syt2 and E-Syt3). However, the function of extended-synaptotagmins is different to that of synaptotagmins, which are involved in secretory vesicle tethering to the plasma membrane and exocytosis. The extended-synaptotagmins are located to the endoplasmic reticulum (ER), and tether this organelle to the plasma membrane via their C2 domains. They transport glycerolipids between the two bilayers via their lipid-harboring SMP domains. Ca2+ regulates their membrane tethering and lipid transport function [, , ].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 bind phospholipids, inositol polyphosphates, and intracellular proteins. C2 domains with a calcium binding region have negatively charged residues, primarily aspartates, that serve as ligands for calcium ions. This entry represents the second C2 domain in extendend synaptotagmins (and the second and fourth domains in extended E-Syt1), which have a type-I topology []. |
