The Structure of a Binary Complex between a Mammalian Mevalonate Kinase and ATP INSIGHTS INTO THE REACTION MECHANISM AND HUMAN INHERITED DISEASE

Abstract Mevalonate kinase catalyzes the ATP-dependent phosphorylation of mevalonic acid to form mevalonate 5-phosphate, a key intermediate in the pathways of isoprenoids and sterols. Deficiency in mevalonate kinase activity has been linked to mevalonic aciduria and hyperimmunoglobulinemia D/periodic fever syndrome (HIDS). The crystal structure of rat mevalonate kinase in complex with MgATP has been determined at 2.4-A resolution. Each monomer of this dimeric protein is composed of two domains with its active site located at the domain interface. The enzyme-bound ATP adopts an anti conformation, in contrast to the syn conformation reported for Methanococcus jannaschii homoserine kinase. The Mg2+ ion is coordinated to both β- and γ-phosphates of ATP and side chains of Glu193 and Ser146. Asp204is making a salt bridge with Lys13, which in turn interacts with the γ-phosphate. A model of mevalonic acid can be placed near the γ-phosphoryl group of ATP; thus, the C5 hydroxyl is located within 4 A from Asp204, Lys13, and the γ-phosphoryl of ATP. This arrangement of residues strongly suggests: 1) Asp204 abstracts the proton from C5 hydroxyl of mevalonate; 2) the penta-coordinated γ-phosphoryl group may be stabilized by Mg2+, Lys13, and Glu193; and 3) Lys13 is likely to influence the pK a of the C5 hydroxyl of the substrate. V377I and I268T are the most common mutations found in patients with HIDS. Val377 is located over 18 A away from the active site and a conservative replacement with Ile is unlikely to yield an inactive or unstable protein. Ile-268 is located at the dimer interface, and its Thr substitution may disrupt dimer formation.