Table 1.

Intrinsic Ca2+-binding affinities of wild-type and mutant C2A domains

Ca2+-binding siteWTD232ND238N
  • Ca2+ binding to the isolated wild-type (WT) C2A domain of synaptotagmin 1 and the D232N and D238N point mutants of the C2A domain was monitored by1H–15N HSQC acquired with 150–165 μm of purified recombinant C2A domains. Dissociation constants were calculated from the Ca2+titrations as described (Fernández-Chacón et al., 2001) and are expressed in micromolar Ca2+.

  • F1-a Calculated from the Ca2+ dependence of the 15N chemical shift of the K200 NH resonance between 0 and 600 μm total Ca2+.

  • F1-b Calculated from the Ca2+ dependence of the 1H chemical shift of the S235 NH resonance.

  • F1-c Only a lower limit can be estimated because the site was not saturated at the highest Ca2+ concentration used (40 mm).

  • F1-d Estimated based on the fact that no cross-peak movement corresponding to this site is observed up to 40 mm Ca2+.