Pig2p is a putative type-1 protein phosphatase (PP1) targeting subunit that tethers the Glc7p type-1 protein phosphatase to the Gsy2p glycogen synthase (2). Pig2p binds Gsy2p in two-hybrid analyses, and displays 30% similarity to Gip2p, another putative regulatory subunit of the protein phosphatase Glc7p (1).

One traditional analysis has shown that a pig2 null mutant in the EG328-1A strain background accumulates normal levels of glycogen (1). However, in a large-scale study using a homozygous diploid deletion series in the BY4743 strain background, a pig2 null mutant accumulates less glycogen than wild type (4). glc7-109 mutants display increased levels of glycogen, and this hyperglycogen phenotype is partially retained in pig1 gac1 gip2 triple null glc7-109 mutants, indicating that Pig2p may be a redundant targeting subunit capable of targeting Glc7p-109 to Gsy2p (2).

Gac1p, Pig1p, Pig2p and Gip2p are the only four yeast proteins that share a conserved segment of 25 residues, designated the GVNK motif, which is also found in mammalian type-1 protein phosphatase targeting subunits (1). Pig2p also possesses two short regions of similarity to the Rhizopus glucoamylase precursor AMYG, and to various mammalian glycogen-associated regulatory subunits of protein phosphatase 1 (1), including rabbit RG RAB and human PPP1R3, mutations in which are associated with non-insulin-dependent diabetes mellitus (5).

Last updated: 2005-10-25