Figure 1.

Crystal structure of SNARE-induced Ca²⁺-bound Syt3. (a) Showing a ribbon diagram of the C2AB fragment of Syt3 including the C2A (magenta) and C2B (yellow) domains, and bound Ca²⁺ ions (gray spheres). (b) Side view illustrating that the Ca²⁺-binding loops of both C2 domains emerge from the same side of the molecule. Residues Lys427, Lys557, and Arg556 are shown as sticks. (c) Superposition of the crystal structures of SNARE-induced Ca²⁻-bound (magenta and yellow) and Ca²⁺-free (blue, PDB ID 1DQV²⁰) Syt3 C2AB fragments. We aligned structures by superposition of the Cα positions of their respective C2A domains (see cartoon where the “+” sign indicates the Ca²⁺-binding regions).