Identification of the major postsynaptic density protein as homologous with the major calmodulin-binding subunit of a calmodulin-dependent protein kinase.
The major postsynaptic density protein (mPSDp), comprising greater than 50% of postsynaptic density (PSD) protein, is an endogenous substrate for calmodulin-dependent phosphorylation as well as a calmodulin-binding protein in PSD preparations. The results in this investigation indicate that mPSDp is highly homologous with the major calmodulin-binding subunit (p) of tubulin-associated calmodulin-dependent kinase (TACK), and that PSD fractions also contain a protein homologous with the sigma-subunit of TACK. Homologies between mPSDp and a 63,000 dalton PSD protein and the rho- and sigma-subunits of TACK were established by the following criteria: (1) identical apparent molecular weights; (2) identical calmodulin-binding properties; (3) manifestation of Ca2+-calmodulin-stimulated autophosphorylation; (4) identical isoelectric points; (5) identical calmodulin binding and autophosphorylation patterns on two-dimensional gels; (6) homologous two-dimensional tryptic peptide maps; and (7) similar phosphoamino acid-specific phosphorylation of tubulin. The results suggest that mPSDp is a calmodulin-binding protein involved in modulating protein kinase activity in the postsynaptic density and that a tubulin kinase system homologous with TACK exists in a membrane-bound form in the PSD.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D007525:Isoelectric Focusing; D046911:Macromolecular Substances; D009419:Nerve Tissue Proteins / Q000032:analysis*; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D014357:Trypsin / Q000378:metabolism; D014404:Tubulin / Q000378:metabolism
D002147:Calmodulin; D046911:Macromolecular Substances; D009419:Nerve Tissue Proteins; D014404:Tubulin; C033652:postsynaptic density proteins; D011494:Protein Kinases; D014357:Trypsin; D002118:Calcium