Protein tyrosine phosphatases: X-ray crystallographic observation of cysteinyl-phosphate reaction intermediate

Abstract

The chapter considers some of the theoretical and practical parameters for optimizing the accumulation of the phosphoryl-enzyme intermediate in solution because this is a prerequisite for trapping the phosphoryl enzyme in the crystalline state. An enzyme-catalyzed reaction is a multistep event, with each step governed by discrete kinetic rate constants. The formation of phosphoryl-enzyme intermediates is a necessary component of numerous enzymatic reactions that involve phosphoryl-transfer processes. These include, for example, the dephosphorylation of phosphoamino acids by the members of the protein tyrosine phosphatase (PTP) superfamily. The opposing activities of the protein phosphatases and protein kinases regulate the overall level of intracellular protein phosphorylation, an essential process of the signal transduction pathways triggered by hormones, mitogens, and oncogenes that regulate growth, differentiation, and proliferation. The PTPs are a large and diverse family of enzymes that comprise tyrosine-specific transmembrane receptor-like PTPs and soluble cytosolic proteins, as well as the subfamily of dual-specificity phosphatases (DSPs). The DSPs are related in terms of structure and catalytic mechanism to the tyrosine-specific phosphatases but differ in their substrate selectivity, being capable of dephosphorylating all three phosphoamino acids.