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Expanding the active pH range of Escherichia coli glutamate decarboxylase by breaking the cooperativeness

Paper ID Volume ID Publish Year Pages File Format Full-Text
20828 43193 2013 5 PDF Available
Title
Expanding the active pH range of Escherichia coli glutamate decarboxylase by breaking the cooperativeness
Abstract

Bacterial glutamate decarboxylase (GAD) transforms glutamate into γ-aminobutyric acid (GABA) with the consumption of a proton. The enzyme is active under acidic environments only and sharply loses its activity as pH approaches neutrality with concomitant structural deformation. In an attempt to understand better the role of this cooperative loss of activity upon pH shifts, we prepared and studied a series of GAD site-specific mutants. In this report, we show that the cooperativeness was kept intact by at least two residues, Glu89 and His465, of which Glu89 is newly identified to be involved in the cooperativity system of GAD. Double mutation on these residues not only broke the cooperativity in the activity change but also yielded a mutant GAD that retained the activity at neutral pH. The resulting mutant GAD that was active at neutral pH inhibited the cell growth in a glycerol medium by converting intracellular Glu into GABA in an uncontrolled manner, which explains in part why the cooperativeness of GAD has to be kept by several layers of safety keepers. This unexpected result might be utilized to convert a low-valued by-product of biodiesel production, glycerol, into value-added product, GABA.

Keywords
Glutamate decarboxylase; Enzyme cooperativeness; Gamma-aminobutyric acid; Enzyme engineering; pH-range expansion
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Expanding the active pH range of Escherichia coli glutamate decarboxylase by breaking the cooperativeness
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Bioscience and Bioengineering - Volume 115, Issue 2, February 2013, Pages 154–158
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us