Investigation of the functional contributions of invariant serine residues in yeast mevalonate diphosphate decarboxylase.

Alignment of more than 20 deduced sequences for mevalonate diphosphate decarboxylase (MDD) indicates that serines 34, 36, 120,121, 153, and 155 are invariant residues that map within a proposed interdomain active site cleft. To test possible active site roles for these invariant serines, each has been mutated to alanine. S34A exhibits limited solubility and impaired binding of the fluorescent ATP analogue, trinitrophenyl-ATP (TNP-ATP), suggesting that Ser-34 substitution destabilizes proper enzyme folding.