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Title
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Observation of a tetrahedral reaction intermediate in the HIV-1 protease-substrate complex.
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Authors
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M.Kumar,
V.Prashar,
S.Mahale,
M.V.Hosur.
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Ref.
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Biochem J, 2005,
389,
365-371.
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PubMed id
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Abstract
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HIV-1 protease is an effective target for the design of drugs against AIDS. To
help this process of drug design, three-dimensional structures have been
determined of complexes between HIV-1 protease and a variety of transition-state
analogue inhibitors. The true transition state, however, has not been
structurally characterized. The crystal structure of the C95M/C1095A HIV-1
protease tethered dimer shows a distinctive feature in which the two flaps of
the enzyme are in a 'closed conformation' even in the unliganded state. This
unique feature has been utilized here to study the structure of HIV-1 protease
complexed to an oligopeptide substrate of amino acid sequence
His-Lys-Ala-Arg-Val-Leu*NPhe-Glu-Ala-Nle-Ser (where * denotes the cleavage site,
and NPhe and Nle denote p-nitrophenylalanine and norleucine residues
respectively). The X-ray structure of the complex refined against 2.03 A (0.203
nm) resolution synchrotron data shows that the substrate is trapped as a
tetrahedral reaction intermediate in the crystal. The hydrogen-bonding
interactions between the reaction intermediate and the catalytic aspartates are
different from those observed previously using transition-state analogues. The
reaction intermediate did not dissociate to release the products, possibly due
to the inflexibility introduced in the flaps when the enzyme is packed inside
crystals.
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