Figure 1.

Both the C₂A and C₂B domains of synaptotagmin have conserved hydrophobic residues at the tip of the Ca²⁺-binding pocket. A, Alignment of synaptotagmin I from rat and Drosophila. Bars indicate β-sheets, asterisks indicate the conserved hydrophobic residues mutated in this study, dots indicate Ca²⁺-binding residues, and open circles with a plus indicate conserved basic residues. Within the alignment, conserved residues are shown in gray and identical residues are boxed. B, Schematic representation of loops 1 and 3 in Drosophila that form the Ca²⁺-binding pockets of each C₂ domain. D₁–D₅ and E₅ indicate Ca²⁺-binding residues. F*, M, I*, and V indicate hydrophobic residues at the tip of the Ca²⁺-binding pockets.