Characterization of mevalonate kinase V377I, a mutant implicated in defective isoprenoid biosynthesis and HIDS/periodic fever syndrome

The list of diseases linked to defects in lipid metabolism has recently bee n augmented by the addition of hyperimmunoglobulinemia D and periodic fever syndrome (HIDS: MIM 260920), which are correlated with depressed levels of mevalonate kinase activity [1,2] and protein [1]. More specifically, a V37 7I substitution has been proposed to account for this disease. We observed that V377 appears to be far from invariant in eukaryotic mevalonate kinases . Prokaryotic mevalonate kinases are lower in molecular weight and several terminate prior to residue 377 of the eukaryotic proteins. These observatio ns prompted our direct test of the impact of V377 on activity and protein s tability by engineering a V377I mutation in a recombinant human mevalonate kinase. The mutant protein has been isolated and kinetically characterized. In comparison with wild-type enzyme, V377I exhibits only modest difference s (notably greater than or equal to 6-fold inflation of K-m(MVA)) that do n ot account for the diminished mevalonate kinase activity assayed in HIDS ce ll extracts. Moreover, thermal inactivation (50 degreesC) of isolated wild- type and V377I enzymes demonstrates little difference in stability between these proteins. We conclude that a single V377I substitution is unlikely to explain the observation of depressed mevalonate kinase stability and catal ytic activity in HIDS. (C) 2001 Elsevier Science B.V. All rights reserved.