Analyzing protein tyrosine phosphatases by phosphotyrosine analog integration

Reversible protein phosphorylation plays a central role in cellular signal transduction and is a focus of biomedical studies. However, it is a challenging task to study the effects of protein phosphorylation in the presence of protein phosphatase activities, especially for protein tyrosine phosphatases SHP1, SHP2 and LMW-PTP, which are themselves regulated by protein tyrosine phosphorylation. Expressed protein ligation, by combining chemical peptide synthesis with recombinant protein expression, allows for site-specific unnatural modifications of semisynthetic proteins. In this review, we describe how semisynthetic proteins were prepared to incorporate nonhydrolyzable phosphotyrosine analogs, and utilized in combination with site-directed mutagenesis and other means to elucidate regulatory mechanisms of protein tyrosine phosphatases.