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A mutant lactose repressor with altered inducer and operator binding parameters.

A E Chakerian, M Pfahl, J S Olson

Journal of Molecular Biology

|May 5, 1985

Summary

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A mutation in the Escherichia coli lactose repressor protein (BG185) impairs inducer binding kinetics. This suggests the Ala81Val change locks the protein in a closed conformation, affecting its function.

Area of Science:

Molecular Biology
Protein Structure and Function
Biochemistry

Background:

The lactose repressor protein controls the lac operon in Escherichia coli.
Mutations can alter protein structure and function, impacting gene regulation.
Understanding repressor-inducer interactions is crucial for gene expression studies.

Purpose of the Study:

To investigate the functional consequences of a specific mutation (Ala81Val) in the Escherichia coli lactose repressor protein.
To characterize the inducer binding properties of the mutant BG185 repressor.
To elucidate the structural implications of the Ala81Val substitution on repressor-inducer complex formation.

Main Methods:

Spectroscopic analysis (fluorescence spectroscopy)

Related Experiment Videos

Chemical measurements

Direct binding assays

Kinetic measurements of inducer binding

Main Results:

The BG185 mutant protein showed similar overall properties to the wild-type repressor-inducer complex.
Inducer binding kinetics for BG185 were significantly slower (over two orders of magnitude) than wild-type.
Fluorescence spectral shifts upon inducer binding were identical for mutant and wild-type, indicating direct effects on nearby tryptophan residues.
The mutation likely fixes the protein in a closed, sugar-binding conformation.

Conclusions:

The Ala81Val mutation in the lactose repressor protein markedly impairs the structural transitions necessary for efficient inducer binding.
The mutation appears to stabilize a closed conformation, analogous to bacterial sugar-binding proteins.
Direct effects on tryptophan fluorescence suggest localized conformational changes rather than global shifts.