Amino acid sequence and expression of the hepatic glycogen-binding (G_L-subunit of protein phosphatase-1

A full-length cDNA encoding the putative hepatic glycogen-binding (GL) subunit of protein phosphatase-1 (PP1) was isolated from a rat liver library. The deduced amino acid sequence (284 residues, 32.6 kDa) was 23% identical (39% similar) to the N-terminal region of the glycogen-binding (GM) subunit of PP1 from striated muscle. The similarities between GM and GL were most striking between residues 63-86, 144-166 and 186-227 of human GM (∼40% identity), nearly all the identities with the putative yeast homologue GAC1 being located between 144-166 and 186-227. The cDNA was expressed in E. coli, and the expressed protein transformed the properties of PP1 to those characteristic of the hepatic glycogen-associated enzyme. These experiments establish that the cloned protein is GL.