synaptotagmin-like protein 2; breast cancer-associated antigen SGA-72M; exophilin-4 (SYTL2, KIAA1597, SGA72M, SLP2, SLP2A)
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Function
- may act as Rab effector protein
- vesicle trafficking
- isoform 1
- acts as a RAB27A effector protein
- role in cytotoxic granule exocytosis in lymphocytes
- required for cytotoxic granule docking at the immunologic synapse
- highly susceptible to proteolytic degradation
- stabilized by the interaction with RAB27A
- isoform 4
- binds phosphatidylserine & phosphatidylinositol-4,5-bisphosphate (PIP2) & promotes the recruitment of glucagon-containing granules to the cell membrane in pancreatic alpha cells
- binding to phosphatidylserine is inhibited by Ca+2
- binding to PIP2 is Ca+2 insensitive
Structure
- the RabBD domain mediates interaction with RAB27A & recruitment on to vesicular structures in cytotoxic T-cells
- the C2 1 domain mediates binding to phosphatidylserine & phosphatidylinositol 4,5-bisphosphate (PIP2) & localization to the cell membrane
- contains 2 C2 domains
- contains 1 RabBD (Rab-binding) domain
Compartment
- isoform 1:
- cytoplasm, cell membrane
- recruited on vesicular structures in cytotoxic T-lymphocytes by RAB27A (GTP bound)
- isoform 4:
- cell membrane
- in pancreatic alpha cells, distributed in both peripheral & anterior regions
- localizes on the glucagon granules in the cell periphery
Alternative splicing
named isoforms=12
Expression
- isoform 1
- expressed in hematopoietic lineages
- strong expression in CD4 & CD8 T-lymphocytes. It
- also widely expressed in nonhematopoietic tissues
- expressed in hematopoietic lineages
- isoform 4 is expressed in pancreatic alpha cells
- isoform 5 is expressed only in nonhematopoietic tissues