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Structural biology of the purine biosynthetic pathway 总被引:1,自引:0,他引:1
Purine biosynthesis requires ten enzymatic transformations to generate inosine monophosphate. PurF, PurD, PurL, PurM, PurC,
and PurB are common to all pathways, while PurN or PurT, PurK/PurE-I or PurE-II, PurH or PurP, and PurJ or PurO catalyze the
same steps in different organisms. X-ray crystal structures are available for all 15 purine biosynthetic enzymes, including
7 ATP-dependent enzymes, 2 amidotransferases and 2 tetrahydrofolate-dependent enzymes. Here we summarize the structures of
the purine biosynthetic enzymes, discuss similarities and differences, and present arguments for pathway evolution. Four of
the ATP-dependent enzymes belong to the ATP-grasp superfamily and 2 to the PurM superfamily. The amidotransferases are unrelated,
with one utilizing an N-terminal nucleophileglutaminase and the other utilizing a triad glutaminase. Likewise the tetrahydrofolate-dependent
enzymes are unrelated. Ancestral proteins may have included a broad specificity enzyme instead of PurD, PurT, PurK, PurC,
and PurP, and a separate enzyme instead of PurM and PurL.
Received 26 May 2008; received after revision 30 June 2008; accepted 9 July 2008 相似文献
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Glutamate synthase is a complex iron-sulfur flavoprotein that forms l-glutamate from l-glutamine and 2-oxoglutarate. It participates
with glutamine synthetase in ammonia assimilation processes. The known structural and biochemical properties of glutamate
synthase from Azospirillum brasilense, a nitrogen-fixing bacterium, will be discussed in comparison to those of the ferredoxin-dependent enzyme from photosynthetic
tissues and of the eukaryotic reduced pyridine nucleotide-dependent form of glutamate synthase in order to gain insight into
the mechanism of the glutamate synthase reaction. Sequence analyses also revealed that the small subunit of bacterial glutamate
synthase may be the prototype of a novel class of flavin adenine dinucleotide- and iron-sulfur-containing oxidoreductase widely
used as an enzyme subunit or domain to transfer reducing equivalents from NAD(P)H to an acceptor protein or protein domain.
Received 10 November 1998, received after revision 10 December 1998; accepted 10 December 1998 相似文献
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