| Abstract
| - Protein tyrosine phosphatases (PTPases) are signal-transducing enzymes that dephosphorylateintracellular proteins that have phosphorylated tyrosine residues. It has been demonstratedthat protein tyrosine phosphatase 1B (PTP1B) is an attractive therapeutic target because ofits involvement in regulating insulin sensitivity (Elcheby et al.Science1999, 283, 1544−1548).The identification of a second binding site in PTP1B (Puius et al. , Proc. Natl. Acad. Sci. U.S.A.1997, 94, 13420−13425) suggests a new strategy for inhibitor design, where appropriatecompounds may be made to simultaneously occupy both binding sites to gain much higheraffinity and selectivity. To test this hypothesis and gain further insights into the structuralbasis of inhibitor binding, we have determined the crystal structure of PTP1B complexed withtwo non-peptidyl inhibitors, 4 and 5, both of which contain two aryl difluoromethylenephosphonic acid groups, a nonhydrolyzable phosphate mimetic. The structures were determinedand refined to 2.35 and 2.50 Å resolution, respectively. Although one of the inhibitors seemsto have satisfied the perceived requirement for dual binding, it did not bind both the activesite and the adjacent noncatalytic binding site as expected. The second or distal phosphonategroup instead extends into the solvent and makes water-mediated interactions with Arg-47.The selectivity of the more potent of these two inhibitors, as well as four other inhibitors bearingtwo such phosphate mimetics for PTP1B versus seven other PTPases, was examined. In general,selectivity was modest to good when compared to PTPases Cdc25a, PTPmeg-1, PTPβ, and CD45.However, selectivity was generally poor when compared to other PTPases such as SHP-1, SHP-2, and especially TCPTP, for which almost no selectivity was found. The implications theseresults have concerning the utility of dual-binding inhibitors are discussed.
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