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1e1c

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{{STRUCTURE_1e1c| PDB=1e1c | SCENE= }}
{{STRUCTURE_1e1c| PDB=1e1c | SCENE= }}
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'''METHYLMALONYL-COA MUTASE H244A MUTANT'''
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===METHYLMALONYL-COA MUTASE H244A MUTANT===
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==Overview==
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Adenosylcobalamin-dependent methylmalonyl-CoA mutase catalyzes the interconversion of methylmalonyl-CoA and succinyl-CoA via radical intermediates generated by substrate-induced homolysis of the coenzyme carbon-cobalt bond. From the structure of methylmalonyl-CoA mutase it is evident that the deeply buried active site is completely shielded from solvent with only a few polar contacts made between the protein and the substrate. Site-directed mutants of amino acid His244, a residue close to the inferred site of radical chemistry, were engineered to investigate its role in catalysis. Two mutants, His244Ala and His244Gln, were characterized using kinetic and spectroscopic techniques. These results confirmed that His244 is not an essential residue. However, compared with that of the wild type, k(cat) was lowered by 10(2)- and 10(3)-fold for the His244Gln and His244Ala mutants, respectively, while the K(m) for succinyl-CoA was essentially unchanged in both cases. The primary kinetic tritium isotope effect (k(H)/k(T)) for the His244Gln mutant was 1.5 +/- 0.3, and tritium partitioning was now found to be dependent on the substrate used to initiate the reaction, indicating that the rearrangement of the substrate radical to the product radical was extremely slow. The His244Ala mutant underwent inactivation under aerobic conditions at a rate between 1 and 10% of the initial rate of turnover. The crystal structure of the His244Ala mutant, determined at 2.6 A resolution, indicated that the mutant enzyme is unaltered except for a cavity in the active site which is occupied by an ordered water molecule. Molecular oxygen reaching this cavity may lead directly to inactivation. These results indicate that His244 assists directly in the unusual carbon skeleton rearrangement and that alterations in this residue substantially lower the protection of reactive radical intermediates during catalysis.
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(as it appears on PubMed at http://www.pubmed.gov), where 10924114 is the PubMed ID number.
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{{ABSTRACT_PUBMED_10924114}}
==About this Structure==
==About this Structure==
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[[Category: Isomerase]]
[[Category: Isomerase]]
[[Category: Mutase]]
[[Category: Mutase]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jun 30 23:58:41 2008''

Revision as of 20:58, 30 June 2008

Image:1e1c.png

Template:STRUCTURE 1e1c

METHYLMALONYL-COA MUTASE H244A MUTANT

Template:ABSTRACT PUBMED 10924114

About this Structure

1E1C is a Protein complex structure of sequences from Propionibacterium freudenreichii subsp. shermanii. Full crystallographic information is available from OCA.

Reference

Protection of radical intermediates at the active site of adenosylcobalamin-dependent methylmalonyl-CoA mutase., Thoma NH, Evans PR, Leadlay PF, Biochemistry. 2000 Aug 8;39(31):9213-21. PMID:10924114

Page seeded by OCA on Mon Jun 30 23:58:41 2008

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