Identification of the molecular trigger for allosteric activation in glycogen phosphorylase

Activation of protein function through phosphorylation can be mimicked by the engineering of specific metal binding sites. The addition of two histidine residues to glycogen phosphorylase allows enzymatic activation by transition metals in a cooperative and allosteric manner. Crystal structures of the metallo-enzyme have been determined and show that the structural transition induced upon metal binding (Ni2+) is, in part, analogous to the mode of activation of the native enzyme. The designed metal activation site allows assignment of the structural changes which trigger activation in this allosteric enzyme and, further, provide insight into the evolutionary development of multiple activation sites.