4eb3
Crystal structure of IspH in complex with iso-HMBPP
Structural highlights
FunctionISPH_ECOLI Converts 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate into isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). Is also involved in penicillin tolerance and control of the stringent response. Seems to directly or indirectly interact with RelA to maintain it in an inactive form during normal growth.[1] [2] [3] Publication Abstract from PubMedThe [4Fe-4S] protein IspH in the methylerythritol phosphate isoprenoid biosynthesis pathway is an important anti-infective drug target, but its mechanism of action is still the subject of debate. Here, by using electron paramagnetic resonance (EPR) spectroscopy and (2)H, (17)O, and (57)Fe isotopic labeling, we have characterized and assigned two key reaction intermediates in IspH catalysis. The results are consistent with the bioorganometallic mechanism proposed earlier, and the mechanism is proposed to have similarities to that of ferredoxin, thioredoxin reductase, in that one electron is transferred to the [4Fe-4S](2+) cluster, which then performs a formal two-electron reduction of its substrate, generating an oxidized high potential iron-sulfur protein (HiPIP)-like intermediate. The two paramagnetic reaction intermediates observed correspond to the two intermediates proposed in the bioorganometallic mechanism: the early pi-complex in which the substrate's 3-CH(2)OH group has rotated away from the reduced iron-sulfur cluster, and the next, eta(3)-allyl complex formed after dehydroxylation. No free radical intermediates are observed, and the two paramagnetic intermediates observed do not fit in a Birch reduction-like or ferraoxetane mechanism. Additionally, we show by using EPR spectroscopy and X-ray crystallography that two substrate analogues (4 and 5) follow the same reaction mechanism. Are free radicals involved in IspH catalysis? An EPR and crystallographic investigation.,Wang W, Wang K, Span I, Jauch J, Bacher A, Groll M, Oldfield E J Am Chem Soc. 2012 Jul 11;134(27):11225-34. doi: 10.1021/ja303445z. Epub 2012, Jun 28. PMID:22687151[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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