Figure 2.

The C₂A^D2E mutation inhibits Ca²⁺ binding by C₂A without disrupting protein folding. A, ITC analysis of Ca²⁺ binding to the isolated C₂A domain of WT and mutant Drosophila synaptotagmin 1; a representative Ca²⁺ titration is shown (n = 3). C₂A^WT bound three calcium ions (Table 1). The heat of binding of Ca²⁺ by C₂A^D2E was so small that the data could not be accurately fit. B, C₂A^D2E is correctly folded. The CD spectra of the mutant domain (C₂A^D2E) was identical to wild-type (C₂A^WT).