Premium
NMR measurement of the off rate from the first calcium‐binding site of the synaptotagmin I C 2 A domain
Author(s) -
Millet Oscar,
Bernadó Pau,
Garcia Jesús,
Rizo Josep,
Pons Miquel
Publication year - 2002
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(02)02508-5
Subject(s) - calcium , chemistry , synaptotagmin i , synaptotagmin 1 , dissociation constant , nuclear magnetic resonance , dissociation (chemistry) , diffusion , analytical chemistry (journal) , receptor , thermodynamics , biochemistry , membrane , physics , chromatography , synaptic vesicle , vesicle , organic chemistry
The off rate from the first calcium‐binding site of the C 2 A domain of synaptotagmin I, a putative calcium receptor in neurotransmitter release, has been determined by 15 N‐nuclear magnetic resonance relaxation dispersion measurements. The exchange rate was obtained by fitting the dependence of the transverse relaxation rates on the interval between 180° pulses in relaxation‐compensated CPMG experiments at 3.2 μM calcium concentration. The measured k ex is 2.0×10 3 s −1 . The calcium on rate of 3.5±1×10 7 s −1 , determined from the measured off rate and the dissociation constant (5.3×10 −5 M), is close to the diffusion limit. These results are consistent with the proposed role of synaptotagmin I as a calcium sensor in release, but suggest that additional factors may help to accelerate the diffusion of Ca 2+ to the sensor.