A Trojan horse transition state analogue generated by MgF3- formation in an enzyme active site.

Nicola J Baxter, Luis F Olguin, Marko Golicnik, Guoqiang Feng, Andrea M Hounslow, Wolfgang Bermel, G Michael Blackburn, Florian Hollfelder, Jonathan P Waltho, Nicholas H Williams

Index: Proc. Natl. Acad. Sci. U. S. A. 103(40) , 14732-7, (2006)

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Abstract

Identifying how enzymes stabilize high-energy species along the reaction pathway is central to explaining their enormous rate acceleration. beta-Phosphoglucomutase catalyses the isomerization of beta-glucose-1-phosphate to beta-glucose-6-phosphate and appeared to be unique in its ability to stabilize a high-energy pentacoordinate phosphorane intermediate sufficiently to be directly observable in the enzyme active site. Using (19)F-NMR and kinetic analysis, we report that the complex that forms is not the postulated high-energy reaction intermediate, but a deceptively similar transition state analogue in which MgF(3)(-) mimics the transferring PO(3)(-) moiety. Here we present a detailed characterization of the metal ion-fluoride complex bound to the enzyme active site in solution, which reveals the molecular mechanism for fluoride inhibition of beta-phosphoglucomutase. This NMR methodology has a general application in identifying specific interactions between fluoride complexes and proteins and resolving structural assignments that are indistinguishable by x-ray crystallography.