WHY IS PHOSPHONODIFLUOROMETHYL PHENYLALANINE A MORE POTENT INHIBITORYMOIETY THAN PHOSPHONOMETHYL PHENYLALANINE TOWARD PROTEIN-TYROSINE PHOSPHATASES

The phosphonodifluoromethyl phenylalanine (F(2)Pmp) is superior to pho sphonomethyl phenylalanine (Pmp) as a non-hydrolyzable phosphotyrosine (pTyr) mimetic. The difluoromethyl moiety increases the inhibitory po tency of a F(2)Pmp-containing peptide over a Pmp-containing counterpar t by 1000-fold toward the protein tyrosine phosphatase (PTPase), PTP1. Fluorine substitution at the methylene carbon have the double effect of lowering the phosphonate pK(a2) as well as introducing hydrogen bon ding interactions similar to the phosphate ester oxygen in pTyr. The i nhibition of PTP1-catalyzed dephosphorylation reaction by both the F(2 )Pmp and Pmp-containing peptides did not vary as a function of pH. The data indicate that both the monoanion and the dianion forms of the ph osphonate bind PTP1 with equal efficiency. Thus, the better binding by the F(2)Pmp-peptide as compared to the Pmp-peptide is not due to the difference in pK(a2). Taken together, these results offer an explanati on for the increased affinity of F(2)Pmp for PTP1. The two fluorine at oms in F(2)Pmp may be able to interact with active site residues in PT P1 in a fashion analogous to that involving the phenolic oxygen and si de chains in the active site of PTP1. K-i measurements for a simple ph osphonic acid, Pmp- and F(2)Pmp-containing peptides suggest that altho ugh the principal recognition element is F(2)Pmp itself, the surroundi ng amino acids are required for high affinity binding. Comparative ana lysis of the inhibition of PTP1, PTP alpha and LAR by F(2)Pmp-containi ng peptides suggests that selective, tight-binding PTPase inhibitors c an be developed. (C) 1995 Academic Press, Inc.