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2z25

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[[Image:2z25.gif|left|200px]]
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{{STRUCTURE_2z25| PDB=2z25 | SCENE= }}
{{STRUCTURE_2z25| PDB=2z25 | SCENE= }}
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'''Thr110Val dihydroorotase from E. coli'''
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===Thr110Val dihydroorotase from E. coli===
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==Overview==
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Dihydroorotase (DHOase) catalyzes the reversible cyclization of N-carbamyl-l-aspartate (CA-asp) to l-dihydroorotate (DHO) in the de novo biosynthesis of pyrimidine nucleotides. Two different conformations of the surface loop (residues 105-115) were found in the dimeric Escherichia coli DHOase crystallized in the presence of DHO (PDB code 1XGE). The loop asymmetry reflected that of the active site contents of the two subunits: the product, DHO, was bound in the active site of one subunit and the substrate, CA-asp, in the active site of the other. In the substrate- (CA-asp-) bound subunit, the surface loop reaches in toward the active site and makes hydrogen bonds with the bound CA-asp via two threonine residues (Thr109 and Thr110), whereas the loop forms part of the surface of the protein in the product- (DHO-) bound subunit. To investigate the relationship between the structural states of this loop and the catalytic mechanism of the enzyme, a series of mutant DHOases including deletion of the flexible loop were generated and characterized kinetically and structurally. Disruption of the hydrogen bonds between the surface loop and the substrate results in significant loss of catalytic activity. Furthermore, structures of these mutants with low catalytic activity have no interpretable electron density for parts of the flexible loop. The structure of the mutant (Delta107-116), in which the flexible loop is deleted, shows only small differences in positions of other substrate binding residues and in the binuclear zinc center compared with the native structure, yet the enzyme has negligible activity. The kinetic and structural analyses suggest that Thr109 and Thr110 in the flexible loop provide productive binding of substrate and stabilize the transition-state intermediate, thereby increasing catalytic activity.
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(as it appears on PubMed at http://www.pubmed.gov), where 17711307 is the PubMed ID number.
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{{ABSTRACT_PUBMED_17711307}}
==About this Structure==
==About this Structure==
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[[Category: Hydrolase]]
[[Category: Hydrolase]]
[[Category: Tim barrel]]
[[Category: Tim barrel]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun Jul 27 21:11:42 2008''

Revision as of 18:11, 27 July 2008

Image:2z25.png

Template:STRUCTURE 2z25

Thr110Val dihydroorotase from E. coli

Template:ABSTRACT PUBMED 17711307

About this Structure

2Z25 is a Single protein structure of sequence from Escherichia coli. Full crystallographic information is available from OCA.

Reference

Kinetic and structural analysis of mutant Escherichia coli dihydroorotases: a flexible loop stabilizes the transition state., Lee M, Maher MJ, Christopherson RI, Guss JM, Biochemistry. 2007 Sep 18;46(37):10538-50. Epub 2007 Aug 21. PMID:17711307

Page seeded by OCA on Sun Jul 27 21:11:42 2008

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