Glycogen targeting protein subunit

Organizing glucose disposal emerging roles of the glycogen targeting subunits of protein phosphatase-1. Diabetes 49, 1967-1977. 

The G subimit of protein phosphatase I, occurring in the glycogen-boimd form, is considered as its localization subimit. The G subunit enables targeted localization of the catalytic subunit of protein phosphatase I to glycogen so that a close spatial orientation of protein phosphatase and its substrates, the enzymes of glycogen metabolism, is created (see 7.6.2). 

J. Wu, J. Liu, I. Thompson, C.J. Oliver, S. Shenolikar, and D.L. Brautigan. 1998. A conserved domain for glycogen binding in protein phosphatase-1 targeting subunits FEBSLett. 439 185-191. (PuhMed)... 

Figure 25-14 Mechanism of insulin action. Binding of insulin to the extracellular a-subunit of the insulin receptor induces autophosphorylation of the -subunit of the receptor and phosphorylation of selected intracellular proteins, such as She and the IRS family,These latter phosphoproteins interact with other targets, thereby activating phosphorylation cascades, which result in glucose uptake (in adipose tissue and skeletal muscle), glucose metabolism, synthesis (of glycogen, iipid, and proteins), enhanced gene expression, cell growth, and differentiation, p, protein phosphorylation aPKC, atypical protein kinase C, See text for details.

Johnson DF, Moorhead G, Caudwell FB, Cohen P, Chen YH, Chen MX, Cohen PT (1996) Identification of protein-phosphatase-1-binding domains on the glycogen and myofibrillar targetting subunits. Eur J Biochem 239 317-325... 

Increased epinephrine activates PKA, which phosphorylates a subunit of PPl and thus reduces the ability of PPl to act on its protein targets. Furthermore, inhibitor 1 is also phosphorylated by PKA so that it too decreases PPl activity, albeit by a different mechanism. Inactivated PPl leads to increased levels of activated (phosphorylated) phosphorylase and inactivated (phosphorylated) glycogen synthase. Glycogen breakdown would be stimulated under these conditions. 

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