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PDBsum entry 1ct9
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Three-Dimensional structure of escherichia coli asparagine synthetase b: a short journey from substrate to product.
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Authors
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T.M.Larsen,
S.K.Boehlein,
S.M.Schuster,
N.G.Richards,
J.B.Thoden,
H.M.Holden,
I.Rayment.
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Ref.
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Biochemistry, 1999,
38,
16146-16157.
[DOI no: ]
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PubMed id
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Abstract
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Asparagine synthetase B catalyzes the assembly of asparagine from aspartate,
Mg(2+)ATP, and glutamine. Here, we describe the three-dimensional structure of
the enzyme from Escherichia colidetermined and refined to 2.0 A resolution.
Protein employed for this study was that of a site-directed mutant protein,
Cys1Ala. Large crystals were grown in the presence of both glutamine and AMP.
Each subunit of the dimeric protein folds into two distinct domains. The
N-terminal region contains two layers of antiparallel beta-sheet with each layer
containing six strands. Wedged between these layers of sheet is the active site
responsible for the hydrolysis of glutamine. Key side chains employed for
positioning the glutamine substrate within the binding pocket include Arg 49,
Asn 74, Glu 76, and Asp 98. The C-terminal domain, responsible for the binding
of both Mg(2+)ATP and aspartate, is dominated by a five-stranded parallel
beta-sheet flanked on either side by alpha-helices. The AMP moiety is anchored
to the protein via hydrogen bonds with O(gamma) of Ser 346 and the backbone
carbonyl and amide groups of Val 272, Leu 232, and Gly 347. As observed for
other amidotransferases, the two active sites are connected by a tunnel lined
primarily with backbone atoms and hydrophobic and nonpolar amino acid residues.
Strikingly, the three-dimensional architecture of the N-terminal domain of
asparagine synthetase B is similar to that observed for glutamine
phosphoribosylpyrophosphate amidotransferase while the molecular motif of the
C-domain is reminiscent to that observed for GMP synthetase.
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