3csu
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(New page: 200px<br /><applet load="3csu" size="450" color="white" frame="true" align="right" spinBox="true" caption="3csu, resolution 1.88Å" /> '''CATALYTIC TRIMER OF ...)
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Revision as of 17:30, 20 November 2007
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CATALYTIC TRIMER OF ESCHERICHIA COLI ASPARTATE TRANSCARBAMOYLASE
Overview
The lack of knowledge of the three-dimensional structure of the trimeric, catalytic (C) subunit of aspartate transcarbamoylase (ATCase) has impeded, understanding of the allosteric regulation of this enzyme and left, unresolved the mechanism by which the active, unregulated C trimers are, inactivated on incorporation into the unliganded (taut or T state), holoenzyme. Surprisingly, the isolated C trimer, based on the 1.9-A, crystal structure reported here, resembles more closely the trimers in the, T state enzyme than in the holoenzyme:bisubstrate-analog complex, which, has been considered as the active, relaxed (R) state enzyme. Unlike the C, trimer in either the T state or bisubstrate-analog-bound holoenzyme, the, isolated C trimer lacks 3-fold symmetry, and the active sites are, partially disordered. The flexibility of the C trimer, contrasted to the, highly constrained T state ATCase, suggests that regulation of the, holoenzyme involves modulating the potential for conformational changes, essential for catalysis. Large differences in structure between the active, C trimer and the holoenzyme:bisubstrate-analog complex call into question, the view that this complex represents the activated R state of ATCase.
About this Structure
3CSU is a Single protein structure of sequence from Escherichia coli with CA as ligand. Active as Aspartate carbamoyltransferase, with EC number 2.1.3.2 Full crystallographic information is available from OCA.
Reference
Assessment of the allosteric mechanism of aspartate transcarbamoylase based on the crystalline structure of the unregulated catalytic subunit., Beernink PT, Endrizzi JA, Alber T, Schachman HK, Proc Natl Acad Sci U S A. 1999 May 11;96(10):5388-93. PMID:10318893
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