Synaptotagmin is the Ca2+ sensor for exocytosis. We have crystallized the two tandem C2 domains of human synaptotagmin. The crystal structure shows clear signs of inter-domain interaction.

Fuson KL, Montes M, Robert JJ, Sutton RB. Structure of human synaptotagmin 1 C2AB in the absence of Ca2+ reveals a novel domain association.Biochemistry. 2007 Nov 13;46(45):13041-8. Epub 2007 Oct 23.