Phosphorylase kinase, gamma catalytic subunit (IPR002291)
Short name: Phosph_kin_gamma
Overlapping homologous superfamilies
- Protein kinase-like domain superfamily (IPR011009)
- Calcium/calmodulin-dependent/calcium-dependent protein kinase (IPR020636)
- Phosphorylase kinase, gamma catalytic subunit (IPR002291)
Protein phosphorylation, which plays a key role in most cellular activities, is a reversible process mediated by protein kinases and phosphoprotein phosphatases. Protein kinases catalyse the transfer of the gamma phosphate from nucleotide triphosphates (often ATP) to one or more amino acid residues in a protein substrate side chain, resulting in a conformational change affecting protein function. Phosphoprotein phosphatases catalyse the reverse process. Protein kinases fall into three broad classes, characterised with respect to substrate specificity [PMID: 3291115]:
- Serine/threonine-protein kinases
- Tyrosine-protein kinases
- Dual specificity protein kinases (e.g. MEK - phosphorylates both Thr and Tyr on target proteins)
Protein kinase function is evolutionarily conserved from Escherichia coli to human [PMID: 12471243]. Protein kinases play a role in a multitude of cellular processes, including division, proliferation, apoptosis, and differentiation [PMID: 12368087]. Phosphorylation usually results in a functional change of the target protein by changing enzyme activity, cellular location, or association with other proteins. The catalytic subunits of protein kinases are highly conserved, and several structures have been solved [PMID: 15078142], leading to large screens to develop kinase-specific inhibitors for the treatments of a number of diseases [PMID: 15320712].
Phosphorylase B kinase (EC:188.8.131.52) belongs to a family of proteins involved in glycogen biosynthesis [PMID: 7857257]. The protein has a subunit composition of (alpha, beta, gamma, delta)4, where the alpha and beta subunits are regulatory, delta is calmodulin, and the gamma subunit is catalytic. The enzyme is believed to have a dual role, the first is connected with glycogen degradation via phosphorylation of glycogen phosphorylase; the second controls glycogen biosynthesis on the sarcoplasmic reticular membrane more directly by phosphorylation, and thus inhibition, of glycogen synthase [PMID: 7729511].
The gamma catalytic chain contains three domains; one protein kinase and two calmodulin-binding domains. Calcium and magnesium ions, together with cyclic AMP, positively affect the efficiency of the enzyme, which is believed to be associated with its auto-kinase activity [PMID: 7857257, PMID: 8590760].
The full extent of the effects of deficiencies in this enzyme in humans is unknown; but case studies have been documented [PMID: 8944243, PMID: 9553951, PMID: 7562285] that detail symptoms as mild as 'exercise intolerance' [PMID: 8944243], to infant mortality arising from floppy infant syndrome [PMID: 9553951].
- PR01049 (PHOSPHBKNASE)