Ca(2+)-dependent conformational change in synaptotagmin I.
Synaptotagmin I is a Ca2+/phospholipid binding protein of synaptic vesicles with a proposed function as a Ca2+ sensor in synaptic vesicle exocytosis. Using controlled partial proteolysis as an assay, we now show that synaptotagmin I undergoes a conformational change as a function of Ca2+ binding. As observed for phospholipid binding, Ba2+ and Sr2+ but not Mg2+, substitute for Ca2+ in effecting this conformational change. The first C2 domain from synaptotagmin I that represents the Ca(2+)-dependent phospholipid binding domain of synaptotagmin also undergoes a Ca(2+)-dependent change in controlled partial proteolysis. In contrast, no effect of Ca2+ was observed with mutant C2 domains containing point mutations that abolish Ca2+ binding. The Ca2+ concentration dependence of the effect of Ca2+ on proteolysis mirrors the Ca2+ dependence of phospholipid binding. The conformational shift in synaptotagmin I caused by Ca2+/phospholipid binding could be the basis for its Ca(2+)-regulated function in triggering neurotransmitter release.
Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas 75235.
B A
BA
Davletov
T C
TC
Südhof
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins; D005089:Exocytosis; D006868:Hydrolysis; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D051381:Rats; D013572:Synaptic Vesicles / Q000378:metabolism; D050863:Synaptotagmin I; D050857:Synaptotagmins
D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D050863:Synaptotagmin I; C494312:Syt1 protein, rat; D050857:Synaptotagmins; D002118:Calcium