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PMID: 16782782 Published · ppublish English Journal Article Research Support, N.I.H., Extramural Research Support, Non-U.S. Gov't

Ca2+-triggered simultaneous membrane penetration of the tandem C2-domains of synaptotagmin I.

Biophysical journal ·Vol. 91 ·No. 5 ·2006-09-01 ·Pages 1767-77

Hui E, Bai J, Chapman ER

Abstract

Synaptotagmin I (syt), a transmembrane protein localized to secretory vesicles, functions as a Ca2+ sensor that facilitates SNARE-mediated membrane fusion. The cytoplasmic domain of syt harbors two C2-domains designated C2A and C2B. Upon binding Ca2+, C2A and C2B partially penetrate into membranes that contain anionic phospholipids. However, it is unknown whether these tandem C2-domains engage membranes at the same time, in a sequential manner, or in a mutually exclusive manner. We have used site-directed fluorescent probes to monitor the penetration of syt's C2-domains into phosphatidylserine-harboring lipid bilayers. We report that, in response to Ca2+, C2A and C2B copenetrate into these bilayers with diffusion-limited kinetics. Membrane penetration was more efficient when synthetic rather than natural phospholipids were used to prepare bilayers. The membrane penetration activity of the intact cytoplasmic domain of syt (C2A-C2B) exhibits significant resistance to changes in ionic strength. In contrast, the ability of isolated C2B to bind membranes in response to Ca2+ can be disrupted by subtle changes in ionic strength. Tethering C2B to a mutant version of C2A that does not bind Ca2+ or membranes significantly increases the stability of Ca2+.C2B.membrane complexes, confirming that C2A affects the membrane-binding properties of the adjacent C2B domain.

MeSH Terms
Calcium/chemistry Lipid Bilayers/chemistry Membranes, Artificial Permeability Phospholipids/chemistry Protein Structure, Tertiary Synaptotagmin I/chemistry
Chemicals
Lipid Bilayers Membranes, Artificial Phospholipids Synaptotagmin I Syt1 protein, rat Calcium
Authors & Affiliations
3 authors, click to expand affiliations / ORCID
Hui Enfu
Howard Hughes Medical Institute and Department of Physiology, University of Wisconsin School of Medicine, Madison, Wisconsin 53706, USA.
Bai Jihong
Chapman Edwin R
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Article Info
Journal
Biophysical journal
Abbr.
Biophys J
ISSN
0006-3495
DOI
10.1529/biophysj.105.080325
Published
2006-09-01
Epub
2006-00-16
Pages
1767-77
Language
English
Region
United States
NLM ID
0370626
PMCID
PMC1544279
Subset
IM
Grants
NIGMS NIH HHS · R01 GM056827 · United States
NIMH NIH HHS · R01 MH061876 · United States
NIGMS NIH HHS · GM 56827 · United States
NIMH NIH HHS · MH61876 · United States
External Links
PubMed source DOI: 10.1529/biophysj.105.080325 PMC Full Text View journal details
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