This Article Full Text Full Text (PDF) Supplemental Material Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by García, R. A. Articles by Godwin, H. A. Search for Related Content PubMed PubMed Citation Articles by García, R. A. Articles by Godwin, H. A.

High Metal Concentrations Are Required for Self-Association of Synaptotagmin II

Ricardo A. García ^* and Hilary Arnold Godwin ^* 

^* Department of Biochemistry, Molecular Biology, and Cell Biology, and Department of Chemistry, Northwestern University, Evanston, Illinois

Correspondence: Address reprint requests to Hilary Arnold Godwin, Dept. of Chemistry, Northwestern University, 2145 Sheridan Rd., Evanston IL 60208-3113. Tel.: 847-467-3543; Fax: 847-491-7713; E-mail: h-godwin{at}northwestern.edu.

Several members of the synaptotagmin (syt) family of vesicle proteins have been proposed to act as Ca²⁺ sensors on synaptic vesicles. The mechanism by which calcium activates this class of proteins has been the subject of controversy, yet relatively few detailed biophysical studies have been reported on how isoforms other than syt I respond to divalent metal ions. Here, we report a series of studies on the response of syt II to a wide range of metal ions. Analytical ultracentrifugation studies demonstrate that Ca²⁺ induces protein dimerization upon exposure to 5 mM Ca²⁺. Whereas Ba²⁺, Mg²⁺, or Sr²⁺ do not potentiate self-association as strongly as Ca²⁺, Pb²⁺ triggers self-association of syt II at concentrations as low as 10 µM. Partial proteolysis studies suggest that the various divalent metals cause different changes in the conformation of the protein. The high calcium concentrations required for self-association of syt II suggest that the oligomerized state of this protein is not a critical intermediate in vesicle fusion; however, low-affinity calcium sites on syt II may play a critical role in buffering calcium at the presynaptic active zone. In addition, the high propensity of lead to oligomerize syt II offers a possible molecular explanation for how lead interferes with calcium-evoked neurotransmitter release.