ORGANIC
LETTERS
2011
Vol. 13, No. 21
5912–5915
Study of IspH, a Key Enzyme in the
Methylerythritol Phosphate Pathway Using
Fluoro-Substituted Substrate Analogues
Youli Xiao,† Wei-chen Chang,‡ Hung-wen Liu,*,‡ and Pinghua Liu*,†
Department of Chemistry, Boston University, Boston, Massachusetts 02215,
United States, and Division of Medicinal Chemistry, College of Pharmacy, and
Department of Chemistry and Biochemistry, University of Texas at Austin, Austin,
Texas 78712, United States
h.w.liu@mail.utexas.edu; pinghua@bu.edu
Received September 21, 2011
ABSTRACT
IspH, a [4Fe-4S]-cluster-containing enzyme, catalyzes the reductive dehydroxylation of 4-hydroxy-3-methyl-butenyl diphosphate (HMBPP) to
isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) in the methylerythritol phosphate pathway. Studies of IspH using fluoro-
substituted substrate analogues to dissect the contributions of several factors to IspH catalysis, including the coordination of the HMBPP C4ꢀOH
group to the ironꢀsulfur cluster, the H-bonding network in the active site, and the electronic properties of the substrates, are reported.
IspH is a [4Fe-4S]-cluster-containing enzyme found in
the newly discovered isoprene biosynthetic pathway known
as the methylerythritol phosphate (MEP) pathway.1 It
catalyzes the last step of the MEP pathway by reductive
dehydroxylation of the C4ꢀOH group of 4-hydroxy-3-
methyl-butenyl diphosphate (HMBPP, 1) to isopentenyl
diphosphate (IPP, 2) and dimethylallyl diphosphate
(DMAPP, 3, Figure 1), which are the two building blocks
for all isoprenoids.2,3 While the MEP pathway is not
present in humans, it is essential for many pathogenic
microorganisms. Therefore, the enzymes involved in this
pathway are attractive new targets for antimicrobial
drugs.3,4 Early results showed that its labile [4Fe-4S]
cluster contains a unique iron site,5ꢀ10 to which the
C4ꢀOH group of HMBPP binds (4 in Scheme 1).6,7,11 The
bound HMBPP adopts a hairpin conformation in the active
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€
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† Boston University.
‡ University of Texas at Austin.
€
(10) Grawert, T.; Kaiser, J.; Zepeck, F.; Laupitz, R.; Hecht, S.;
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Life Sci. 2004, 61, 1401–1426.
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Amslinger, S.; Schramek, N.; Schleicher, E.; Weber, S.; Haslbeck, M.;
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r
10.1021/ol202559r
Published on Web 10/07/2011
2011 American Chemical Society