Contribution of Amino Acid Side Chains to Sugar Binding Specificity in a Galactokinase, Gal1p, and a Transcriptional Inducer, Gal3p

The crystal structure of the yeast galactokinase, Gal1p, in the presence of its substrates has been solved recently. We systematically mutated each of the amino acid side chains that, from the structure, are implicated to be involved in direct contact with the hydroxyl groups of the galactose ring....

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Bibliographic Details
Published in:The Journal of biological chemistry 2006-06, Vol.281 (25), p.17150-17155
Main Authors: Sellick, Christopher A., Reece, Richard J.
Format: Article
Language:English
Subjects:
Crystallography, X-Ray
Galactokinase - chemistry
Galactokinase - genetics
Galactokinase - metabolism
Galactose - chemistry
Kinetics
Ligands
Models, Molecular
Molecular Conformation
Mutation
Protein Binding
Protein Conformation
Protein Structure, Tertiary
Saccharomyces cerevisiae - metabolism
Saccharomyces cerevisiae Proteins - chemistry
Saccharomyces cerevisiae Proteins - genetics
Saccharomyces cerevisiae Proteins - metabolism
Substrate Specificity
Transcription Factors - chemistry
Transcription Factors - genetics
Transcription Factors - metabolism
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Summary:The crystal structure of the yeast galactokinase, Gal1p, in the presence of its substrates has been solved recently. We systematically mutated each of the amino acid side chains that, from the structure, are implicated to be involved in direct contact with the hydroxyl groups of the galactose ring. One of these mutations, D62A, abolished all detectable galactokinase activity but retained the ability to use d-glucose as a substrate. Mutation of Asp-62 to either leucine, phenylalanine, or histidine resulted in the formation of protein with similar characteristics to D62A. Yeast galactokinase is highly similar to Gal3p, the ligand sensor and transcriptional inducer of the GAL genes. Equivalent mutations in Gal3p also abolished its ability to respond to galactose and uncovered its ability to respond to d-glucose. It therefore appears that Gal1p and Gal3p respond to their substrates in a similar, perhaps identical, fashion. This work also validates the approach of screening for mutants in an easily assayable system prior to mutant analysis in a more experimentally difficult transcriptional regulator.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M602086200