| Description |
Archaea utilize the mevalonate (MVA) pathway for the biosynthesis of isopentenyl diphosphate (IPP) and its isomer, dimethylallyl diphosphate (DMAPP), the two building blocks of all isoprenoids. The archaeal MVA pathway deviates from the classical eukaryotic MVA pathway in the two-step conversion of mevalonate phosphate to IPP by utilizing a putative phosphomevalonate decarboxylase and the recently discovered isopentenyl phosphate kinase (IPK). The latter catalyzes the ATP-dependent phosphoryl transfer reaction to isopentenyl phosphate (IP) to form IPP. Chen and Poulter recently characterized IPKs from Thermoplasma acidophilum (THA) and Methanothermobacter thermautotrophicus (MTH), using its substrate IP and other small molecule isoprenoid monophosphates. In this dissertation, we report the first crystal structures of THA and MTH IPKs in complex with their substrates and products. The structures reveal key active site residues involved in substrate binding and catalysis. We also describe the promiscuity of IPK towards fosfomycin, an antibiotic produced in Streptomyces and the substrate of the fosfomycin resistance enzyme, FomA. The structure of FomA is highly homologous to that of IPK, indicating a possible evolutionary relationship between the two enzymes. Finally, we describe four THA IPK mutants with kinase activities toward the longer chain isoprenoids geranyl phosphate (GP) and farnesyl phosphate (FP), achieved by mutations located in the IP binding site. |
