Purified GST-SV2A (1-160) protein was phosphorylated in vitro by purified GST- TTBK2 (1 - 316) WT and GST-TTBK2 (1 - 316) KD. Increasing amounts of phosphorylated GST-SV2A (1 - 160) (0 ng, 10 ng, 50 ng, 100 ng) were subjected to SDS-PAGE and each phosphospecific antibody was tested by their ability to detect those phosphosites.