Specific Partial Reduction of Geranylgeranyl Diphosphate by an Enzyme from the Thermoacidophilic Archaeon Sulfolobus acidocaldarius Yields a Reactive Prenyl Donor, Not a Dead-End Product

Abstract

Geranylgeranyl reductase from Sulfolobus acidocaldarius was shown to catalyze the reduction of geranylgeranyl groups in the precursors of archaeal membrane lipids, generally reducing all four double bonds. However, when geranylgeranyl diphosphate was subjected to the reductase reaction, only three of the four double bonds were reduced. Mass spectrometry and acid hydrolysis indicated that the allylic double bond was preserved in the partially reduced product derived from geranylgeranyl diphosphate. Thus, the reaction product was shown to be phytyl diphosphate, which is a substrate for archaeal prenyltransferases, unlike the completely reduced compound phytanyl diphosphate.

A novel geranylgeranyl reductase from the methanogenic archaeon Methanosarcina acetivorans displays unique regiospecificity

“…It was intriguing that the reductase was highly specific to the x-double bond of a geranylgeranyl group. This site-specific reduction was unprecedented and different from the reduction patterns of known archaeal GGRs that typically reduce a geranylgeranyl group to a phytanyl group [14][15][16][17] and of plant-type GGRs that convert it into a phytyl group [18]. The mechanisms responsible for these distinct patterns will be discussed later.…”

“…4B). Based on the previous data of similar radio-TLC analyses of the GGR reaction products from GGPP and GGGP [16], the slight distance between the spots of the substrate and the product suggested that only one double bond of the geranylgeranyl chain was saturated. This observation was consistent with the fact that tetrahydro-DGGGP-glycerol produced in E. coli cells harboring pBAD-ALB4-MA1492 had one saturated isoprene unit per isoprenoid hydrocarbon chain (Fig.…”

“…geranylgeranyl reductase (GGR). Archaeal GGRs reduce all double bonds in the geranylgeranyl groups of substrate lipids to yield lipids with fully saturated phytanyl groups [14][15][16][17]. They are homologous with the plant GGRs that are responsible for the biosynthesis of chlorophyll, phylloquinone and tocopherol, which catalyze the partial reduction of a geranylgeranyl group to give a phytyl group [18].…”

“…They are homologous with the plant GGRs that are responsible for the biosynthesis of chlorophyll, phylloquinone and tocopherol, which catalyze the partial reduction of a geranylgeranyl group to give a phytyl group [18]. Like plant GGRs, when reducing geranylgeranyl diphosphate (GGPP), which is a prenyl donor substrate for archaeal membrane lipid biosynthesis, GGR from a thermoacidophilic archaeon Sulfolobus solfataricus leaves its a-isoprene unit unsaturated so that the product phytyl diphosphate is available for subsequent prenyl transfer steps [16]. The other archaeal PRs, which have been discovered based on their homology to GGR, play roles in various isoprenoid biosynthetic routes.…”

Geranylgeranyl Reductase and Ferredoxin from Methanosarcina acetivorans Are Required for the Synthesis of Fully Reduced Archaeal Membrane Lipid in Escherichia coli Cells

“…This is the first report of the identification of a physiological electron donor for archaeal GGR. On the other hand, previously isolated GGR from a thermoacidophilic archaeon Sulfolobus acidocaldarius (6) catalyzed the partial reduction of archaeal lipid precursors in E. coli without help from archael ferredoxins, suggesting its relatively broad preference toward electron donors. The effect of the archaeal lipid production on the growth of the host bacterial cells was evaluated because they were supposed to possess an unnatural archaeal-bacterial chimeric lipid membrane.…”