In animals, cholesterol is made from 5-carbon building blocks produced by the mevalonate pathway. Drugs that inhibit the mevalonate pathway such as atorvastatin (lipitor) have led to successful treatments for high cholesterol in humans. Another potential target for the inhibition of cholesterol synthesis is mevalonate diphosphate decarboxylase (MDD), which catalyzes the phosphorylation of (R)-mevalonate diphosphate, followed by decarboxylation to yield isopentenyl pyrophosphate. We recently discovered an MDD homolog, mevalonate-3-kinase (M3K) from Thermoplasma acidophilum, which catalyzes the identical phosphorylation of (R)-mevalonate, but without concomitant decarboxylation. Thus, M3K catalyzes half the reaction of the decarboxylase, allowing us to separate features of the active site that are required for decarboxylation from features required for phosphorylation. Here we determine the crystal structure of M3K in the apo form, and with bound substrates, and compare it to MDD structures. Structural and mutagenic analysis reveals modifications that allow M3K to bind mevalonate rather than mevalonate diphosphate. Comparison to homologous MDD structures show that both enzymes employ analogous Arg or Lys residues to catalyze phosphate transfer. However, an invariant active site Asp/Lys pair of MDD previously thought to play a role in phosphorylation is missing in M3K with no functional replacement. Thus, we suggest that the invariant Asp/Lys pair in MDD may be critical for decarboxylation rather than phosphorylation.
<p>More than 60% of pharmaceuticals are related to natural products (NPs), chemicals produced by living organisms.<a></a> Hence, new methods that accelerate natural product discovery are poised to profoundly impact human health. Of the many challenges that remain in natural product discovery, none are as pervasive as structural elucidation, as determination of the molecular structure of a newly discovered natural product can take months, years, or in some cases be altogether unachievable. This challenge can be fueled by lack of sufficient material for spectroscopic analysis, or difficulties in sourcing the producing organism. Even in cases where the analyte is abundant, its physical properties, including molecular structure, can prevent unambiguous structural determination. Here we report the use of microcrystal electron diffraction (MicroED),<a></a> an emerging cryogenic electron microscopy (CryoEM) technique, in combination with genome mining, to address these challenges. As proof-of-principle, we apply these techniques to fischerin (<b>1</b>), an orphan NP isolated more than 30 years ago, with potent cytotoxicity but ambiguous structural assignment.<a></a> We utilize genome mining methods to reconstruct its biosynthetic pathway and highlight the sensitivity of MicroED through the precise determination of the solid-state structure of <b>1</b> from sub-micron thick crystals. This structural solution serves as a powerful demonstration of the synergy of MicroED and synthetic biology in NP discovery, technologies that when taken together will ultimately accelerate the rate at which new drugs are discovered.</p><div><div><p> </p></div></div>
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