MPM-2 epitope sequence is not sufficient for recognition and phosphorylation by ME kinase-H

Monoclonal antibody MPM-2 recognizes a large family of mitotic phosphoproteins in a phosphorylation-dependent manner, The antigenic phosphoepitope, designated the MPM-2 epitope, putatively consists of hydrophobic residue-Thr/Ser-Pro-hydrophobic residue-uncharged/basic residue. In this study, me addressed whether this sequence motif contains all the information necessary for recognition and phosphorylation by the kinase that phosphorylates most MPM-2 antigens, A fusion protein between glutathione S-transferase and a 19-residue peptide that contained two representative MPM-2 epitope sequences overlapping with two potential MAP kinase phosphorylation sites was constructed, Both the MPM-2 epitope sequences in the fusion protein (GST-MPM2) mere phosphorylated by Xenopus egg extract, making the fusion protein MPM-2 reactive, However, while MAP kinase phosphorylated both the MPM-2 epitope sequences, neither ME kinase-H, a good candidate for a major MPM-2 epitope kinase, nor mitotic cdc2 kinase, which is known to phosphorylate certain MPM-2 antigens in vitro, phosphorylated GST-MPM2 to any significant extent. Furthermore, depletion of MAP kinase activity removed most, if not all, of the GST-MPM2 phosphorylating activity from crude Xenopus egg extracts, These results suggest that additional or different structural information than that provided by the deduced MPM-2 epitope sequence is required for recognition and phosphorylation by ME kinase-H or other major MPM-2 epitope kinases, They also offer a valid explanation for selective phosphorylation of certain MPM-2 antigens by R-IAP kinase as well as selective recognition of certain phosphorylated MAP kinase substrates by MPM-2. (C) 1997 Federation of European Biochemical Societies.