STRUCTURE AND FUNCTION OF THE LOW M-R PHOSPHOTYROSINE PROTEIN PHOSPHATASES

Phosphotyrosine protein phosphatases (PTPases) catalyse the hydrolysis of phosphotyrosine residues in proteins and are hence implicated in t he complex mechanism of the control of cell proliferation and differen tiation. The low M-r PTPases are a group of soluble PTPases displaying a reduced molecular mass; in addition, a group of low molecular mass dual specificity (ds)PTPases which hydrolyse phosphotyrosine and phosp hoserine/threonine residues in proteins are known. The enzymes belongi ng to the two groups are unrelated to each other and to other PTPase c lasses except for the presence of a CXXXXXRS/T sequence motif containi ng some of the catalytic residues (active site signature) and for the common catalytic mechanism, clearly indicating convergent evolution. T he low M-r PTPases have a long evolutionary history since microbial (p rokaryotic and eukaryotic) counterparts of both tyrosine-specific and dsPTPases have been described, Despite the relevant number of data rep orted on the structural and catalytic features of a number of low M-r PTPases, only limited information is presently available on the substr ate specificity and the true biological roles of these enzymes, in pro karyotic, yeast and eukaryotic cells. (C) 1997 Elsevier Science B.V.