Insights into the Mechanistic Dichotomy of the Protein Farne-syltransferase Peptide Substrates CVIM and CVLS

摘要

Protein farnesyltransferase (FTase) catalyzes farnesylation of a variety of peptide substrates. ³H α-secondary kinetic isotope effect measurements of two peptide substrates, CVIM and CVLS, are significantly different and have been proposed to reflect a rate-limiting SN2-like transition state with dissociative characteristics for CVIM, while, due to the absence of an isotope effect, CVLS was proposed to have a rate-limiting peptide conformational change. Potential of mean force QM/MM studies coupled with umbrella sampling techniques were performed to further probe this mechanistic dichotomy. We observe the experimentally proposed TS for CVIM, but find that CVLS has a symmetric SN2 TS, which is also consistent with the absence of a ³H α-secondary kinetic isotope effect. These calculations demonstrate facile substrate- dependent alterations in the transition state structure catalyzed by FTase.