Purification and Characterization of PRL Protein Tyrosine Phosphatases

摘要

PRLs constitute a subfamily of protein tyrosine phosphatases(PTPs). In the present paper are reported the molecular cloning, expression, purification, and characterization of all the three members of the PRL enzymes in human and the only PRL in C.elegans. These enzymes were expressed as glutathione S-transferase(GST) fusion proteins in DE3pLysS E.coli cells, and the recombinant fusion proteins were purified on glutathione-Sepharose affinity columns. Having been cleaved with thrombin, GST-free enzymes were further purified on an S-100 Sepharose gel filtration column. The purified proteins show single polypeptide bands on SDS-polyacrylamide gel electrophoresis. With para-nitrophenyl phosphate(p-NPP) as a substrate, PRLs exhibit classical Michaelis-Menten kinetics with Vmax values two orders of magnitude smaller than those of classic PTPs. The responses of PRLs to ionic strength, metal ions and phosphatase inhibitors are similar to those of other characterized PTPs, but their optimal pH values are different. These data thus reveal distinct common biochemical properties of PRL subfamily PTPs as well.