Journal
NATURE STRUCTURAL & MOLECULAR BIOLOGY
Volume 11, Issue 1, Pages 36-44Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/nsmb709
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Funding
- NIGMS NIH HHS [GM 56827] Funding Source: Medline
- NIMH NIH HHS [MH61876] Funding Source: Medline
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [R01GM056827] Funding Source: NIH RePORTER
- NATIONAL INSTITUTE OF MENTAL HEALTH [R01MH061876] Funding Source: NIH RePORTER
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Synaptotagmin-1 (syt), the putative Ca2+ sensor for exocytosis, is anchored to the membrane of secretory organelles. Its cytoplasmic domain is composed of two Ca2+-sensing modules, C(2)A and C2B. Syt binds phosphatidylinositol 4,5-bisphosphate (PIP2), a plasma membrane lipid with an essential role in exocytosis and endocytosis. We resolved two modes of PIP2 binding that are mediated by distinct surfaces on the C2B domain of syt. A novel Ca2+-independent mode of binding predisposes syt to penetrate PIP2-harboring target membranes in response to Ca2+ with submillisecond kinetics. Thus, PIP2 increases the speed of response of syt and steers its membrane-penetration activity toward the plasma membrane. We propose that syt-PIP2 interactions are involved in exocytosis by facilitating the close apposition of the vesicle and target membrane on rapid time scales in response to Ca2+.
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