Weixue Wang - Organometallic mechanism of action and inhibition of the 4Fe-4S isoprenoid biosynthesis protein GcpE (IspG)

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  PNAS  2010 107 (25)  11189-11193; published   ahead of print June 7, 2010,  doi:10.1073/pnas.1000264107


  We report the results of a series of chemical, EPR, ENDOR, and   HYSCORE spectroscopic investigations of the mechanism of action   (and inhibition) of GcpE,   E-1-hydroxy-2-methyl-but-2-enyl-4-diphosphate (HMBPP)   synthase, also known as IspG, an Fe4S4  cluster-containing protein. We find that the epoxide of HMBPP   when reduced by GcpE generates the same transient EPR species as   observed on addition of the substrate,   2-C-methyl-D-erythritol-2, 4-cyclo-diphosphate.   ENDOR and HYSCORE spectra of these transient species (using   2H, 13C and 17O labeled samples)   indicate formation of an Fe-C-H containing organometallic   intermediate, most likely a ferraoxetane. This is then rapidly   reduced to a ferracyclopropane in which the HMBPP product forms   an η2-alkenyl π- (or   π/σ) complex with the 4th Fe in the   Fe4S4 cluster, and a similar “metallacycle”   also forms between isopentenyl diphosphate (IPP) and GcpE. Based   on this metallacycle concept, we show that an alkyne (propargyl)   diphosphate is a good (Ki ∼ 300 nM)   GcpE inhibitor, and supported again by EPR and ENDOR results (a   13C hyperfine coupling of ∼7 MHz), as well as   literature precedent, we propose that the alkyne forms another   π/σ metallacycle, an   η2-alkynyl, or ferracyclopropene. Overall,   the results are of broad general interest because they provide   new mechanistic insights into GcpE catalysis and inhibition, with   organometallic bond formation playing, in both cases, a key role.

  Address (URL): http://www.pnas.org/content/107/25/11189.full?sid=7027ed5e-06d3-4a50-859b-ad4f62 cee294