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1bo8

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[[Image:1bo8.gif|left|200px]]
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{{STRUCTURE_1bo8| PDB=1bo8 | SCENE= }}
{{STRUCTURE_1bo8| PDB=1bo8 | SCENE= }}
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'''THYMIDYLATE SYNTHASE R178T MUTANT'''
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===THYMIDYLATE SYNTHASE R178T MUTANT===
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==Overview==
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In thymidylate synthase, four conserved arginines provide two hydrogen bonds each to the oxygens of the phosphate group of the substrate, 2'-deoxyuridine-5'-monophosphate. Of these, R23, R178, and R179 are far removed from the site of methyl transfer and contribute to catalysis solely through binding and orientation of ligands. These arginines can be substituted by other residues, while still retaining more than 1% activity of the wild-type enzyme. We compared the kinetics and determined the crystal structures of dUMP complexes of three of the most active, uncharged single mutants of these arginines, R23I, R178T, and R179T, and of double mutants (R23I, R179T) and (R178T, R179T). The dramatically higher K(m) for R178T compared to the other two single mutants arises from the effects of R178 substitution on the orientation of dUMP; 10-15-fold increases in for R23I and R178T reflect the role of these residues in stabilizing the closed conformation of TS in ternary complexes. The free energy for productive dUMP binding, DeltaG(S), increases by at least 1 kcal/mol for each mutant, even when dUMP orientation and mobility in the crystal structure is the same as in wild-type enzyme. Thus, the four arginines do not contribute excess positive charge to the PO(4)(-2) binding site; rather, they ideally complement the charge and geometry of the phosphate moiety. More-than-additive increases in DeltaG(S) seen in the double mutants are consistent with quadratic increases in DeltaG(S) predicted for deviations from ideal electrostatic interactions and may also reflect cooperative binding of the arginines to the phosphate oxygens.
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{{ABSTRACT_PUBMED_10653645}}
==About this Structure==
==About this Structure==
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[[Category: Nucleotide biosynthesis]]
[[Category: Nucleotide biosynthesis]]
[[Category: Transferase]]
[[Category: Transferase]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jun 30 19:26:56 2008''

Revision as of 16:26, 30 June 2008

Image:1bo8.png

Template:STRUCTURE 1bo8

THYMIDYLATE SYNTHASE R178T MUTANT

Template:ABSTRACT PUBMED 10653645

About this Structure

1BO8 is a Single protein structure of sequence from Lactobacillus casei. Full crystallographic information is available from OCA.

Reference

Energetic contributions of four arginines to phosphate-binding in thymidylate synthase are more than additive and depend on optimization of "effective charge balance"., Morse RJ, Kawase S, Santi DV, Finer-Moore J, Stroud RM, Biochemistry. 2000 Feb 8;39(5):1011-20. PMID:10653645

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