PHOSPHORYLATION AND DEPHOSPHORYLATION IN THE PROLINE-RICH C-TERMINAL DOMAIN OF MICROTUBULE-ASSOCIATED PROTEIN-2

The C-terminal domain of microtubule-associated protein 2 (MAP2) conta ins a proline-rich region and the tubulin-binding domain. We have gene rated antibodies to follow the phosphorylation state of the proline-ri ch domain. One of these antibodies (no. 305) has been raised against a synthetic peptide P (sequence RTPGTPGTPSY) phosphorylated at the thre onine residues. This sequence is present in the proline-rich region of MAP2 and is phosphorylated in vitro by at least three different proli ne-directed protein kinases: p42(mpk), p34(cdc2), and GSK3 (glycogen s ynthase kinase 3) alpha/beta. The MAP2 sites phosphorylated by these k inases are different, although all of them phosphorylate the C-termina l domain of MAP2 as determined by Staphylococcus aureus V8 protease ma pping. Nonphosphorylated peptide P can be phosphorylated in vitro by a ll three kinases studied with similar efficiency. In high-molecular-ma ss MAP2, this sequence is highly phosphorylated in vivo at the late st ages of rat development. This motif can be rapidly dephosphorylated in vitro by protein-phosphatase 1 (PP1) and 2A (PP2A) catalytic subunits but not by PP2B.