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PDBsum entry 4gwc
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References listed in PDB file
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Key reference
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Title
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Structure and function of non-Native metal clusters in human arginase i.
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Authors
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E.L.D'Antonio,
Y.Hai,
D.W.Christianson.
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Ref.
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Biochemistry, 2012,
51,
8399-8409.
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PubMed id
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Abstract
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Various binuclear metal ion clusters and complexes have been reconstituted in
crystalline human arginase I by removing the Mn(2+)(2) cluster of the wild-type
enzyme with metal chelators and subsequently soaking the crystalline apoenzyme
in buffer solutions containing NiCl(2) or ZnCl(2). X-ray crystal structures of
these metal ion variants are correlated with catalytic activity measurements
that reveal differences resulting from metal ion substitution. Additionally,
treatment of crystalline Mn(2+)(2)-human arginase I with Zn(2+) reveals for the
first time the structural basis for inhibition by Zn(2+), which forms a
carboxylate-histidine-Zn(2+) triad with H141 and E277. The imidazole side chain
of H141 is known to be hyper-reactive, and its chemical modification or
mutagenesis is known to similarly compromise catalysis. The reactive substrate
analogue 2(S)-amino-6-boronohexanoic acid (ABH) binds as a tetrahedral boronate
anion to Mn(2+)(2), Co(2+)(2), Ni(2+)(2), and Zn(2+)(2) clusters in human
arginase I, and it can be stabilized by a third inhibitory Zn(2+) ion
coordinated by H141. Because ABH binds as an analogue of the tetrahedral
intermediate and its flanking transition states in catalysis, this implies that
the various metallo-substituted enzymes are capable of some level of catalysis
with an actual substrate. Accordingly, we establish the following trend for
turnover number (k(cat)) and catalytic efficiency (k(cat)/K(M)): Mn(2+) >
Ni(2+) ≈ Co(2+) ≫ Zn(2+). Therefore, Mn(2+) is required for optimal
catalysis by human arginase I.
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