Table 2.
Equilibrium Ca2+ Titration Parameters of Syt-1 and Syt-7 C2 Domains
| Liposome Composition (Table 1) | Domain | Amount Bound before Ca2+ Addition (%) | Ca1/2 (μM)a | Hill Coefficienta |
|---|---|---|---|---|
| PM | Syt-1 C2A | <5 | 101 ± 2 | 1.7 ± 0.1 |
| PM | Syt-1 C2B | <5 | 14.6 ± 0.6 | 1.3 ± 0.1 |
| PM | Syt-1 C2AB | <5 | 4.5 ± 0.2 | 1.8 ± 0.1 |
| PM(−)PIP2 | Syt-7 C2A | <5 | 4.8 ± 0.4 | 2.2 ± 0.1 |
| PM(−)PIP2 | Syt-7 C2B | 5 ± 1 | 16.0 ± 0.5 | 2.5 ± 0.1 |
| PM(−)PIP2 | Syt-7 C2B C275A | 51 ± 1 | 15.1 ± 0.6 | 2.7 ± 0.2 |
| PM(−)PIP2 | Syt-7 C2AB | 53 ± 3 | 1.2 ± 0.1 | 2.2 ± 0.1 |
| PM | Syt-7 C2A | 6 ± 2 | 4.0 ± 1.0 | 2.2 ± 0.2 |
| PM | Syt-7 C2B | 37 ± 1 | 3.5 ± 0.6 | 0.8 ± 0.1 |
| PM | Syt-7 C2AB | >85 | NDb | NDb |
Uncertainties represent SD from ≥ 3 separate experiments.
a
Ca1/2 and Hill coefficients were obtained from fitting to Eq. 1. Note that these parameters correspond to the population of protein not initially bound to membrane. Parameters could not be determined accurately for Syt-7 C2AB on PM liposomes because of its largely Ca2+-independent profile.
b
ND, no data.