Binds peptides and proteins containing a motif composed of phospho-Ser with proline at the +2 position and arginine or lysine at the -3 position. Antibody binding is phospho-specific and largely independent of other surrounding amino acids. Weakly cross-reacts with sequences containing phospho-Thr instead of phospho-Ser in this motif, with sequences containing phospho-Ser surrounded by Phe at the +1 position, with Arg/Lys at the -3 position. No cross-reactivity is observed with corresponding non-phosphorylated sequences or with other phospho- Thr/Ser/Tyr -containing motifs.