Proteomic identification of Slp4-a interactors by pull-down of GST-tagged Slp4-a truncation variants. (A) Slp4-a interactors were pulled down from HUVEC lysates by incubation with purified GST-Slp4-a-SHD (left) or GST-Slp4-a-ΔSHD (right) coupled to Glutathione-Sepharose. Eluted proteins were separated by SDS-PAGE and analyzed by mass spectrometry using the criteria described in the “Materials and methods” section. Mascot score of putative interactors (GST-Slp4-a-SHD: 429 identifications; GST-Slp4-a-ΔSHD: 324 identifications) was plotted vs number of unique peptides identified. Colored symbols indicate putative interactors that have a ProHits frequency ≤0.0278. Blue symbols represent bait (GST and Slp4-a), green symbols represent interactors shown in the table (bottom) that summarizes the Mascot score, number of unique peptides identified, and the ProHits frequency. (B) Annotated spectrum of the ISEQTYQLSR peptide corresponding to residues 288-297 of STXBP1.