Download MendeleyStructural Basis for the Evolutionary Inactivation of Ca2+ Binding to Synaptotagmin 4
Dai, H., Shin, O.-H., Machius, M., Tomchick, D.R., Sudhof, T.C., Rizo, J.(2004) Nat Struct Mol Biol 11: 844
- PubMed: 15311271
- DOI: https://doi.org/10.1038/nsmb817
- Primary Citation of Related Structures:
1W15, 1W16 - PubMed Abstract:
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.
Organizational Affiliation:
Department of Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390, USA.
