Open AccessIdentification of Protein‐Phosphatase‐1‐Binding Domains on the Glycogen and Myofibrillar Targetting Subunits
Author(s) -
Johnson Deborah F.,
Moorhead Greg,
Caudwell F. Barry,
Cohen Philip,
Chen Yu Hua,
Chen Mao Xiang,
Cohen Patricia T. W.
Publication year - 1996
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1996.0317u.x
Subject(s) - dephosphorylation , glycogen phosphorylase , protein subunit , phosphorylase kinase , phosphorylation , glycogen synthase , glycogen branching enzyme , myosin , protein phosphatase 1 , glycogen , phosphatase , biochemistry , biology , chemistry , gene
The specificity of the catalytic subunit of protein phosphatase‐1 (PP1 c ) is modified by regulatory subunits that target it to particular subcellular locations. Here, we identify PP1 C ‐binding domains on G L and G M the subunits that target PPI C , to hepatic and muscle glycogen, respectively, and on M 110 the subunit that targets PP1 C to smooth muscle myosin. G M ‐(G63–T93) interacted with PP1 C and prevented G L from suppressing the dephosphorylation of glycogen phosphorylase, but it did not dissociate G L from PP1 C or affect other characteristic properties of the PP1G L complex. These results indicate that G L contains two PP1 C ‐binding sites, the region which suppresses the dephosphorylation of glycogen phosphorylase being distinct from that which enhances the dephosphorylation of glycogen synthase. At higher concentrations, G M ‐(G63–N75) had the same effect as G M ‐(G63–T93), but not if Ser67 was phosphorylated by cyclic‐AMP‐dependent protein kinase. Thus, phosphorylation of Ser67 dissociates G M from PP1 C because phosphate is inserted into the PP1 C ‐binding domain of G M M 110 ‐(M1‐E309) and M 110 ‐(M1‐F38), but not M 110 ‐(D39–E309), mimicked the M 110 subunit in stimulating dephosphorylation of the smooth muscle myosin P‐light chain and heavy meromyosin in vitro. However, in contrast to the M 110 subunit and M 110 ‐(M1‐E309), neither M 110 ‐(M1‐F38) nor M 1110 ‐(D39–E309) suppressed the PP C ‐catalysed dephosphorylation of glycogen phosphorylase. These observations suggest that the region which stimulates the dephosphorylation of myosin is situated within the N‐terminal 38 residues of the M 110 subunit, while the region which suppresses the dephosphorylation of glycogen phosphorylase requires the presence of at least part of the region 39–309 which contains seven ankyrin repeats. M 110 ‐(M1‐F38) displaced G L from PPI C while G M ‐(G63‐T93) displaced M 110 from PP1 C in vitro. These observations indicate that the region(s) of PP1 c that interact with G M /G L and M 110 overlap, explaining why different forms of PP1 C contain just a single targetting subunit.