Determinants of allosteric activation of yeast pyruvate kinase and identification of novel effectors using computational screening

We have analyzed the structural determinants of the allosteric activation of yeast pyruvate kinase (YPK) by mutational and kinetic analysis and initiated a structure-based design project to identify novel effecters that modulate its allosteric response by binding to the allosteric site for fructose-1,6-bisphosphate (FBP). The wild type enzyme is strongly activated by fructose-1,6-bisphosphate and weakly activated by both fructose-1-phosphate and fructose-6-phosphate; the strength of the activation response is proportional to the affinity of the allosteric effector. A point mutation within the 6'-phosphate binding loop of the allosteric site (T403E) abolishes activation of the enzyme by fructose-1,6-bisphosphate. The mutant enzyme is also not activated by F1P or F6P. The mutation alone (which incorporates a glutamic acid that is strictly conserved in mammalian M1 isozymes) slightly reduces cooperativity of substrate binding. Three novel compounds were identified that effect the allosteric regulation of YPK by FBP and/or act as novel allosteric activators of the enzyme. One is a physiologically important diphospho sugar, while the other two are hydrophobic compounds that are dissimilar to the natural effector These results demonstrate that novel allosteric effecters may be identified using structure-based screening and are indicative of the potential of this strategy for drug discovery. Regulatory sites are generally more divergent than catalytic sites and therefore offer excellent opportunities for discrimination and specificity between different organisms or between different tissue types.