| Here , we report that WNK 1 selectively binds to and phosphorylates synaptotagmin 2 ( Syt 2 ) within its calcium binding C 2 domains . ^^^ Endogenous WNK 1 and Syt 2 coimmunoprecipitate and colocalize on a subset of secretory granules in INS 1 cells . ^^^ Phosphorylation by WNK 1 increases the amount of Ca2+ required for Syt 2 binding to phospholipid vesicles ; mutation of threonine 202 , a WNK 1 phosphorylation site , partially prevents this change . ^^^ These findings suggest that phosphorylation of Syts by WNK 1 can regulate Ca2+ sensing and the subsequent Ca2+ dependent interactions mediated by Syt C 2 domains . ^^^ |