1w16

Publication Abstract from PubMed

The neuronal protein synaptotagmin 1 functions as a Ca(2+) sensor in exocytosis via two Ca(2+)-binding C(2) domains. The very similar synaptotagmin 4, which includes all the predicted Ca(2+)-binding residues in the C(2)B domain but not in the C(2)A domain, is also thought to function as a neuronal Ca(2+) sensor. Here we show that, unexpectedly, both C(2) domains of fly synaptotagmin 4 exhibit Ca(2+)-dependent phospholipid binding, whereas neither C(2) domain of rat synaptotagmin 4 binds Ca(2+) or phospholipids efficiently. Crystallography reveals that changes in the orientations of critical Ca(2+) ligands, and perhaps their flexibility, render the rat synaptotagmin 4 C(2)B domain unable to form full Ca(2+)-binding sites. These results indicate that synaptotagmin 4 is a Ca(2+) sensor in the fly but not in the rat, that the Ca(2+)-binding properties of C(2) domains cannot be reliably predicted from sequence analyses, and that proteins clearly identified as orthologs may nevertheless have markedly different functional properties.

Structural basis for the evolutionary inactivation of Ca2+ binding to synaptotagmin 4.,Dai H, Shin OH, Machius M, Tomchick DR, Sudhof TC, Rizo J Nat Struct Mol Biol. 2004 Sep;11(9):844-9. Epub 2004 Aug 15. PMID:15311271^[3]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.