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PDBsum entry 2qjs
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References listed in PDB file
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Key reference
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Title
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Structural basis for the role of asp-120 in metallo-Beta-Lactamases.
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Authors
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J.Crisp,
R.Conners,
J.D.Garrity,
A.L.Carenbauer,
M.W.Crowder,
J.Spencer.
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Ref.
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Biochemistry, 2007,
46,
10664-10674.
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PubMed id
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Abstract
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Metallo-beta-lactamases (mbetals) are zinc-dependent enzymes that hydrolyze a
wide range of beta-lactam antibiotics. The mbetal active site features an
invariant Asp-120 that ligates one of the two metal ions (Zn2) and a
metal-bridging water/hydroxide (Wat1). Previous studies show that substitutions
at Asp-120 dramatically affect mbetal activity, but no consensus exists as to
its role in beta-lactam turnover. Here we present crystal structures of the Asn
and Cys mutants of Asp-120 of the L1 mbetal from Stenotrophomonas maltophilia.
Both mutants retain a dinuclear zinc center with Wat1 present. In the
essentially inactive Cys enzyme Zn2 is displaced to a more buried position
relative to that in the wild-type enzyme. In the catalytically impaired Asn
enzyme the coordination of Zn2 is altered, neither it nor Wat1 is coordinated by
Asn-120, and the N-terminal 19 amino acids, important to cooperative
interactions between subunits in the wild-type enzyme, are disordered.
Comparison with the structure of L1 complexed with the hydrolyzed oxacephem
moxalactam suggests that in the Cys mutant Zn2 can no longer make stabilizing
interactions with anionic nitrogen species formed in the hydrolytic reaction.
The diminished activity of the Asn mutant arises from a combination of loss of
intersubunit interactions and impaired proton transfer to, and reduced
interaction of Zn2 with, the substrate amide nitrogen. We conclude that, while
interactions of Asp-120 with active site water molecules are important to proton
transfer and possibly nucleophilic attack by Wat1, its primary role is to
optimally position Zn2 for catalytically important interactions with the charged
amide nitrogen of substrate.
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Secondary reference #1
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Title
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Metal binding asp-120 in metallo-Beta-Lactamase l1 from stenotrophomonas maltophilia plays a crucial role in catalysis.
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Authors
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J.D.Garrity,
A.L.Carenbauer,
L.R.Herron,
M.W.Crowder.
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Ref.
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J Biol Chem, 2004,
279,
920-927.
[DOI no: ]
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PubMed id
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Figure 1.
FIG. 1. Pictorial representation of the active site of
wild-type L1 rendered using Chem Draw Ultra v. 5.0 (top) and
Rasmol 2.6 (bottom). Drawing indicates the proposed interaction
of Asp-120 with the bridging hydroxide and changes affected by
each of the L1 mutants. The coordinates for the Rasmol figure
were obtained from the Protein Data bank using the accession
number 1sml [PDB]
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Figure 6.
FIG. 6. Proposed role of Asp-120 in L1. The interactions of
Zn[2] with substrate CO[2]^– and N groups are excluded in the
structure on the right for clarity.
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The above figures are
reproduced from the cited reference
with permission from the ASBMB
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