Position of Synaptotagmin I at the Membrane Interface: Cooperative Interactions of Tandem C2 Domains
Synaptotagmin I is a synaptic vesicle associated membrane protein that appears to regulate Ca2+-mediated exocytosis. Here, the Ca2+-dependent membrane interactions of a water soluble fragment of synaptotagmin I (C2AB) that contains its two C2 domains (C2A and C2B) were determined using site-directed...
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Published in | Biochemistry (Easton) Vol. 45; no. 32; pp. 9668 - 9674 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
United States
American Chemical Society
15.08.2006
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Subjects | |
Online Access | Get full text |
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Summary: | Synaptotagmin I is a synaptic vesicle associated membrane protein that appears to regulate Ca2+-mediated exocytosis. Here, the Ca2+-dependent membrane interactions of a water soluble fragment of synaptotagmin I (C2AB) that contains its two C2 domains (C2A and C2B) were determined using site-directed spin labeling. Membrane depth parameters were obtained for 19 spin-labeled mutants of C2AB when bound to phosphatidylcholine and phosphatidylserine membranes, and these distance constraints were used in combination with the high-resolution structures of C2A and C2B to generate a model for the membrane orientation and position of synaptotagmin at the bilayer interface. Both C2A and C2B bind to the membrane interface with their first and third Ca2+ binding loops penetrating the membrane interface. The polybasic face of C2B does not interact with the membrane lipid but is available for electrostatic interaction with other components of the fusion machinery. When compared to positions determined previously for the isolated domains, both C2A and C2B have similar orientations; however, the two domains are positioned deeper into the bilayer interior when present in the tandem construct. These data indicate that C2A and C2B do not act independently but influence their mutual membrane penetration. This may explain the occurrence of multiple C2 domains in proteins that function in membrane trafficking and repair. |
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Bibliography: | istex:9813575CF087C3E2498F1C849EA9180D1C2ED133 ark:/67375/TPS-XHK8S0CN-F This work was supported by National Institutes of Health Grants GM 62035 (to D.S.C.), GM72694 (to D.S.C.), and GM64443 (to A.H.) and the ACS Petroleum Research Fund type G (to A.H.). ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0006-2960 1520-4995 |
DOI: | 10.1021/bi060874j |