Probing the reaction mechanism of IspH protein by x-ray structure analysis
Type
ArticleAuthors
Gräwert, TobiasSpan, Ingrid
Eisenreich, Wolfgang
Rohdich, Felix
Eppinger, Jörg

Bacher, Adelbert
Groll, Michael
KAUST Department
Biological & Organometallic Catalysis LaboratoriesBiological and Environmental Sciences and Engineering (BESE) Division
Chemical Science Program
KAUST Catalysis Center (KCC)
Physical Science and Engineering (PSE) Division
Date
2009-12-28Online Publication Date
2009-12-28Print Publication Date
2010-01-19Permanent link to this record
http://hdl.handle.net/10754/561445
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Show full item recordAbstract
Isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) represent the two central intermediates in the biosynthesis of isoprenoids. The recently discovereddeoxyxylulose 5-phosphate pathway generates a mixture of IPP and DMAPP in its final step by reductive dehydroxylation of 1-hydroxy-2-methyl- 2-butenyl 4-diphosphate. This conversion is catalyzed by IspH protein comprising a central iron-sulfur cluster as electron transfer cofactor in the active site. The five crystal structures of IspH in complex with substrate, converted substrate, products and PPi reported in this article provide unique insights into the mechanism of this enzyme. While IspH protein crystallizes with substrate bound to a [4Fe-4S] cluster, crystals of IspH in complex with IPP, DMAPP or inorganic pyrophosphate feature [3Fe-4S] clusters. The IspH:substrate complex reveals a hairpin conformation of the ligand with the C(1) hydroxyl group coordinated to the unique site in a [4Fe-4S] cluster of aconitase type. The resulting alkoxide complex is coupled to a hydrogen-bonding network, which serves as proton reservoir via a Thr167 proton relay. Prolonged x-ray irradiation leads to cleavage of the C(1)-O bond (initiated by reducing photo electrons). The data suggest a reaction mechanism involving a combination of Lewis-acid activation and proton coupled electron transfer. The resulting allyl radical intermediate can acquire a second electron via the iron-sulfur cluster. The reaction may be terminated by the transfer of a proton from the β-phosphate of the substrate to C(1) (affording DMAPP) or C(3) (affording IPP).Citation
Grawert, T., Span, I., Eisenreich, W., Rohdich, F., Eppinger, J., Bacher, A., & Groll, M. (2009). Probing the reaction mechanism of IspH protein by x-ray structure analysis. Proceedings of the National Academy of Sciences, 107(3), 1077–1081. doi:10.1073/pnas.0913045107PubMed ID
20080550PubMed Central ID
PMC2824267Additional Links
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2824267ae974a485f413a2113503eed53cd6c53
10.1073/pnas.0913045107
Scopus Count
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