Acta Crystallographica Section D

Biological Crystallography

Volume 62, Part 7 (July 2006)

research papers

Acta Cryst. (2006). D62, 793-799 [ doi:10.1107/S0907444906017537 ]

Structure of the C2A domain of rabphilin-3A

M. Biadene, P. Montaville, G. M. Sheldrick and S. Becker

Abstract: Rabphilin-3A is a neuronal protein containing a C2-domain tandem. To date, only the structure of the C2B domain has been solved. The crystal structure of the Ca²⁺-free C2A domain has been solved by molecular replacement and refined to 1.92 Å resolution. It adopts the classical C2-domain fold consisting of an eight-stranded antiparallel [beta] -sandwich with type I topology. In agreement with its Ca²⁺-dependent negatively charged membrane-binding properties, this C2 domain contains all the conserved acidic residues responsible for calcium binding. However, the replacement of a conserved aspartic acid residue by glutamic acid allows formation of an additional strong hydrogen bond, resulting in increased rigidity of calcium-binding loop 1. The electrostatic surface of the C2A domain consists of a large positively charged belt surrounded by two negatively charged patches located at both tips of the domain. In comparison, the structurally very similar C2A domain of synaptotagmin I has a highly acidic electrostatic surface, suggesting completely unrelated functions for these two C2A domains.

PDB reference: 2chd

Keywords: C2 domain; rabphilin; calcium binding; C2A.