Control by phosphorylation

The two examples of phospho and dephospho proteins for which structural data were previously available (glycogen phosphorylase and isocitrate dehydrogenase) demonstrated two different mechanisms for control. In glycogen phosphorylase, activation by phosphorylation results in long-range allosteric changes. In isocitrate dehydrogenase, inhibition by phosphorylation is achieved by an electrostatic blocking mechanism with no conformational changes. During the past year, the structures of the phospho and dephospho forms of two more proteins, the cell cycle protein kinase CDK2 and yeast glycogen phosphorylase, have been determined. The new results highlight the importance of the phosphoamino acids both in the organization of local regions of protein structure through phosphate—arginine interactions and in the promotion of long-range conformational responses.