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Title
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Crystal structure of the catalytic trimer of Methanococcus jannaschii aspartate transcarbamoylase.
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Authors
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J.Vitali,
M.J.Colaneri,
E.Kantrowitz.
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Ref.
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Proteins, 2007,
71,
1324-1334.
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PubMed id
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Abstract
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The catalytic trimer of Methanococcus jannaschii aspartate transcarbamoylase is
extremely heat stable, maintaining 75% of its activity after heat treatment for
60 min at 75 degrees C. We undertook its structural analysis in order to
understand the molecular basis of its thermostability and gain insight on how
its catalytic function adapts to high temperature. Several structural elements
potentially contributing to thermostability were identified. These include: (i)
changes in the amino acid composition such as a decrease in the thermolabile
residues Gln and Asn, an increase in the charged residues Lys and Glu, an
increase in Tyr and a decrease in Ala residues; (ii) a larger number of salt
bridges, in particular, the improvement of ion-pair networks; (iii) shortening
of the N-terminus and shortening of three loops. An interesting feature of the
crystal structure is the association of two crystallographically independent
catalytic subunits into a staggered complex with an intertrimer distance of 33.8
A. The active site appears similar to Escherichia coli. Upon substrate binding,
smaller changes in the global orientation of domains and larger conformational
changes of the active site residues are expected as compared to E. coli.
Proteins 2007. (c) 2007 Wiley-Liss, Inc.
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