ARPP-16/ARPP-19 PHOSPHORYLATION BY CDK5

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cyclic-AMP regulated phosphoproteins ARPP-16 and ARPP-19 are PKA substrates found in the neostriatum of the mammalian brain. The amino acid sequences of these proteins are identical except for an extra 16 residues at the N-terminus of ARPP-19. The functions of these proteins are unknown, although phosphorylation of ARPP-16 is strongly stimulated by dopamine. Recent work in the Greengard lab has shown that ARPP-16 and ARPP-19 are phosphorylated by cdk5/p35. We analyzed the in vitro phosphorylated proteins by proteolysis and mass spectrometry to localize the site of cdk5/p35 phosphorylation. We were able to localize the phosphate to one of three Ser/Thr residues, only one of which is within the cdk consensus sequence (S/T)P. Therefore this residue (Ser42 of ARPP-19) is almost certainly phosphorylated by cdk5/p35.