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Titolo:
A SINGLE MUTATION IN THE REGULATORY CHAIN OF ESCHERICHIA-COLI ASPARTATE TRANSCARBAMOYLASE RESULTS IN AN EXTREME T-STATE STRUCTURE
Autore:
WILLIAMS MK; STEC B; KANTROWITZ ER;
Indirizzi:
BOSTON COLL,DEPT CHEM,MERKERT CHEM CTR CHESTNUT HILL MA 02167 BOSTON COLL,DEPT CHEM,MERKERT CHEM CTR CHESTNUT HILL MA 02167
Titolo Testata:
Journal of Molecular Biology
fascicolo: 1, volume: 281, anno: 1998,
pagine: 121 - 134
SICI:
0022-2836(1998)281:1<121:ASMITR>2.0.ZU;2-J
Fonte:
ISI
Lingua:
ENG
Soggetto:
CONCERTED ALLOSTERIC TRANSITION; SITE-DIRECTED MUTAGENESIS; RAY SOLUTION SCATTERING; CRYSTAL-STRUCTURES; EFFECTOR BINDING; QUATERNARY STRUCTURE; 2.8-A RESOLUTION; CATALYTIC CHAIN; NEUTRAL PH; LIGATED-T;
Keywords:
ALLOSTERIC ENZYME; PROTEIN STRUCTURE FUNCTION; NUCLEOTIDE BINDING SITE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
44
Recensione:
Indirizzi per estratti:
Citazione:
M.K. Williams et al., "A SINGLE MUTATION IN THE REGULATORY CHAIN OF ESCHERICHIA-COLI ASPARTATE TRANSCARBAMOYLASE RESULTS IN AN EXTREME T-STATE STRUCTURE", Journal of Molecular Biology, 281(1), 1998, pp. 121-134

Abstract

Kinetic analysis of a mutant version of Escherichia coli aspartate transcarbamoylase in which Thr82 in the regulatory chain (Thr82r) was replaced by Ala results in a shift in the T reversible arrow R equilibrium towards the T-state. In order to understand the structural determinants of this T-state stabilization, the X-ray structure of the unliganded Thr82r --> Ala enzyme was determined at 2.6 Angstrom resolution and refined to a crystallographic residual of 0.175. The structure of the mutant r1 regulatory chain is more similar to that of the r6 regulatory chain than observed for the wild-type enzyme, resulting in a more symmetric structure. Furthermore, the structural changes in the mutantenzyme appears to occur only in the r1 chain, while the r6 chain is almost identical in structure to that of the r6 chain of the wild-type enzyme. The structure of the mutant enzyme exhibits alterations in thesubunit interfaces between the regulatory and catalytic chains, as well as in the interface between the allosteric and zinc domains within the regulatory chain. Moreover, the regulatory dimers are rotated around their respective 2-fold axes approximately 1 degrees beyond the rotation which occurs in the wild-type T-state enzyme. The structural analysis indicates that the enzyme is an ''extreme'' T-state, in which a larger rotation of the regulatory dimers is required for the T to R transition compared to the wild-type enzyme. This extreme T-state structure correlates well with the kinetic parameters determined for the mutant enzyme, showing a stabilized T-state. Furthermore, the structural analysis of the mutant enzyme suggests that replacement of Thr82r withAla alters the local conformation of the nucleotide binding pocket and therefore offers a plausible explanation for the reduced affinity ofthe enzyme for nucleotides. (C) 1998 Academic Press

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 19/09/20 alle ore 12:05:06