3k56

Publication Abstract from PubMed

The biosynthesis of isopentenyl diphosphate (IPP) from either the mevalonate (MVA) or the 1-deoxy-d-xylulose-5-phosphate (DXP) pathway provides the key metabolite for primary and secondary isoprenoid biosynthesis. Isoprenoid metabolism plays crucial roles in membrane stability, steroid biosynthesis, vitamin production, protein localization, defense and communication, photoprotection, sugar transport and glycoprotein biosynthesis. Recently, an alternative branch of the MVA pathway was discovered in the archaeon Methanocaldococcus jannaschii involving a small molecule kinase, isopentenyl phosphate kinase (IPK). IPK belongs to the amino acid kinase (AAK) superfamily. In vitro, IPK phosphorylates isopentenyl monophosphate (IP) in an ATP and Mg2+-dependent reaction producing IPP. Here, we describe crystal structures of IPK from M. jannaschii refined to nominal resolutions of 2.0-2.8 A. Notably, an active site histidine residue (His60) forms a hydrogen bond with the terminal phosphate of both substrate and product. This His residue serves as a marker for a subset of the AAK family that catalyze phosphorylation of phosphate or phosphonate functional groups; the larger family includes carboxyl-directed kinases, which lack this active site residue. Using steady-state kinetic analysis of H60A, H60N and H60Q mutants, the protonated form of the Nepsilon2 nitrogen of His60 was shown to be essential for catalysis, most likely through hydrogen bond stabilization of the transition state accompanying transphosphorylation. Moreover, the structures served as the starting point for the engineering of IPK mutants capable of the chemoenzymatic synthesis of longer chain isoprenoid diphosphates from monophosphate precursors.

Mutation of Archaeal Isopentenyl Phosphate Kinase Highlights Mechanism and Guides Phosphorylation of Additional Isoprenoid Monophosphates.,Dellas N, Noel JP ACS Chem Biol. 2010 Apr 14. PMID:20392112^[3]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.