Changing substrate specificity in a bacterial GDH

What is it about?

Clostridial glutamate dehydrogenase was the first GDH to have its 3-D structure solved, opening the door to rational mutagenesis. The structure identified various key residues, one of which was K89, responsible for recognising and anchoring the sidechain carboxylate of the glutamate substrate. This suggested an obvious test and here the lysine was replaced with leucine producing a mutant enzyme much less able to handle glutamate but better able to acceopt non-polar amino acid substrates.

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Why is it important?

This was one two papers that iniitally explored the amenability of this enzyme to site-directed mutagenesis. Mutant enzyme was well-expressed and soluble and encouraged a long series of further mutational investigations. Occasionally other mutations led to poor expression or more often poor solubility but this was usually corrected e.g. by low-temperature expression.