Sandbox Reserved 767

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This Sandbox is Reserved from Sep 25, 2013, through Mar 31, 2014 for use in the course "BCH455/555 Proteins and Molecular Mechanisms" taught by Michael B. Goshe at the North Carolina State University. This reservation includes Sandbox Reserved 299, Sandbox Reserved 300 and Sandbox Reserved 760 through Sandbox Reserved 779.
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Threonine Dehydratase


Introduction

Threonine dehydratase (TDH) also known as Threonine Ammonia-Lyase and Threonine Deaminase is an enzyme that catalyzes the dehydration of threonine to α-ketobutyrate.

It is the first enzyme in the isoleucine biosynthetic pathway. TDH belongs to the enzyme class EC-4 which cleave C-C, C-O, C-N through hydrolysis or oxidation. TDH [[[EC 4.3.1.19]]] specifically cleaves C-N bonds. DH was first discovered in E.coli around 1965 but has since been purified from other bacterial sources such as Salmonella typhimurium


Structure

Threonine deaminase, purified from Salmonella typhimurium has a molecular weight of about 200,000. It exists as tetramer in its native state and consists of four identical subunits. In the absence of the cofactor pyridoxal phosphate, TDH is seen to dissociate from its tetramer form to about102 kD dimers. TDH contains 2 ACT-like domains

Cofactor For TDH to be catalytically active, pyridoxal phosphate (PLP), its prosthetic group must be attached to TDH. This is initiated when the aldehyde group of PLP forms a Schiff base linkage with the Lys-62 residue of TDH. The electrophilic nitrogen of the pyridine ring of PLP acts as an electron sink where excess electrons can be delocalizes. This effect draws electrons from TDH thereby stabilizing the carbanion intermediate . Below is an illustration of the mechanism of attachment of the cofactor PLP a lysine residue.

Mechanism of Action


Application

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