the structure of glyoxylate carboligase reveals that there is no glutamate in a position to interact with N1’ of thiamine diphosphate, the position homologous to the conserved glutamate is occupied by Val51
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glyoxylate carboligase crystallizes with 6 monomers (a tetramer and a dimer) in an asymmetric unit, vapor diffusion hanging-drop, 2-4 microlitre of protein solution (5-15 mg/ml, 100 micromolar ThDP, 10 micromolar FAD, 1mM MgCl2 and 10 mM quinone Q0) are mixed with equal volume of reservoir solution (0.5% PEG6000, 0.5M NaCl, 40 mM DTT), pH 8.00, temperature 294K, space group P41212, resolution 2.70 A
the mutation leads to a lower catalytic efficiency (3.9%) compared to the wild type enzyme. The enzyme is converted to an acetolactate synthase which can use pyruvate as a substrate with a catalytic efficiency (kcat/Km) of about 20times higher than that of the wild type enzyme
replacement of Val51 by an amino acid with a carboxylate in its side chain (glutamate or aspartate) has striking and significant effects, V51D variant of glyoxylate carboligase undergoes proton exchange at a rate 6fold higher than the wild-type enzyme
the substitution shifts the pH optimum to 6.0-6.2, the mutant is less active (1.2%) than the wild type enzyme (turnover rates are 2 orders of magnitude lower) despite having higher rate of activation of the coenzyme
Glyoxylate carboligase: a unique thiamin diphosphate-dependent enzyme that can cycle between the 4'-aminopyrimidinium and 1,4'-iminopyrimidine tautomeric forms in the absence of the conserved glutamate