Structural and Mutational Analysis of Functional Differentiation between Synaptotagmins-1 and -7
- Baylor
Synaptotagmins are known to mediate diverse forms of Ca{sup 2+}-triggered exocytosis through their C{sub 2} domains, but the principles underlying functional differentiation among them are unclear. Synaptotagmin-1 functions as a Ca{sup 2+} sensor in neurotransmitter release at central nervous system synapses, but synaptotagmin-7 does not, and yet both isoforms act as Ca{sup 2+} sensors in chromaffin cells. To shed light into this apparent paradox, we have performed rescue experiments in neurons from synaptotagmin-1 knockout mice using a chimera that contains the synaptotagmin-1 sequence with its C{sub 2}B domain replaced by the synaptotagmin-7 C{sub 2}B domain (Syt1/7). Rescue was not achieved either with the WT Syt1/7 chimera or with nine mutants where residues that are distinct in synaptotagmin-7 were restored to those present in synaptotagmin-1. To investigate whether these results arise because of unique conformational features of the synaptotagmin-7 C{sub 2}B domain, we determined its crystal structure at 1.44 {angstrom} resolution. The synaptotagmin-7 C{sub 2}B domain structure is very similar to that of the synaptotagmin-1 C{sub 2}B domain and contains three Ca{sup 2+}-binding sites. Two of the Ca{sup 2+}-binding sites of the synaptotagmin-7 C{sub 2}B domain are also present in the synaptotagmin-1 C{sub 2}B domain and have analogous ligands to those determined for the latter by NMR spectroscopy, suggesting that a discrepancy observed in a crystal structure of the synaptotagmin-1 C{sub 2}B domain arose from crystal contacts. Overall, our results suggest that functional differentiation in synaptotagmins arises in part from subtle sequence changes that yield dramatic functional differences.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Sponsoring Organization:
- FOREIGNOTHERUNIVERSITYNIH
- OSTI ID:
- 1026544
- Journal Information:
- PLoS One, Vol. 5, Issue (9) ; 09, 2010
- Country of Publication:
- United States
- Language:
- ENGLISH
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