Mechanism of cis-prenyltransferase reaction probed by substrate analogues

Undecaprenyl pyrophosphate synthase (UPPS) is a cis-type prenyltransferases which catalyzes condensation reactions of farnesyl diphosphate (FPP) with eight isopentenyl pyrophosphate (IPP) units to generate C55 product. In this study, we used two analogues of FPP, 2-fluoro-FPP and [1,1-2H2]FPP, to probe the reaction mechanism of Escherichia coli UPPS. The reaction rate of 2-fluoro-FPP with IPP under single-turnover condition is similar to that of FPP, consistent with the mechanism without forming a farnesyl carbocation intermediate. Moreover, the deuterium secondary KIE of 0.985 ± 0.022 measured for UPPS reaction using [1,1-2H2]FPP supports the associative transition state. Unlike the sequential mechanism used by trans-prenyltransferases, our data demonstrate E. coli UPPS utilizes the concerted mechanism.

Research highlights
► The extremely slow trans-OPPS reaction using 2-Fluoro-FPP supports the sequential mechanism with the carbocation intermediate.
► The similar UPPS reaction rate under single turnover supports the concerted mechanism, without the carbocation intermediate.
► The secondary kinetic isotope effect also supports associate transition state for UPPS reaction, without the carbocation intermediate.