A protein phosphorylation switch at the conserved allosteric site in GP

Area of Science:

• Biochemistry
• Enzymology
• Protein Phosphorylation

Background:

• Yeast glycogen phosphorylase (GP) is a key enzyme in glycogen metabolism.
• Enzyme activation often involves conformational changes and allosteric regulation.
• Phosphorylation is a critical post-translational modification regulating protein function.

Purpose of the Study:

• To elucidate the phosphorylation-initiated mechanism of yeast glycogen phosphorylase (GP) activation.
• To investigate the role of protein refolding and allosteric sites in GP activation.
• To explore the interplay between phosphorylation, dephosphorylation, and ligand binding in enzyme regulation.

Main Methods:

• Biochemical assays to study enzyme kinetics and activity.
• Site-directed mutagenesis to investigate specific amino acid residues.
• Analysis of protein structure and conformational changes upon phosphorylation.

Main Results:

• Phosphorylation of yeast GP initiates local protein refolding, forming a hydrophobic cluster that activates the enzyme.
• The phosphorylated threonine residue is located in the allosteric site.
• Glucose 6-phosphate facilitates dephosphorylation by competing for binding to the allosteric site.
• Mammalian GP activation by adenosine monophosphate shares mechanistic similarities with yeast GP phosphorylation.

Conclusions:

• Yeast GP activation is regulated by a phosphorylation-dependent protein refolding mechanism.
• Allosteric ligands can modulate enzyme activity by influencing phosphorylation/dephosphorylation.
• Regulation of phosphorylation site accessibility is a key factor in controlling enzyme activity.
• Comparative analysis reveals conserved and divergent mechanisms in GP regulation across species.