Cloning, sequencing and functional assignment of the chlorophyll biosynthesis gene, chlP, of Synechocystis sp. PCC 6803

Abstract

A gene from the cyanobacterium Synechocystis sp. PCC 6803 has been cloned and sequenced, and subsequently used to partially complement a bchP mutant of the purple photosynthetic bacterium Rhodobacter sphaeroides. This mutant is blocked in the terminal hydrogenation steps of bchla biosynthesis and possesses only bchl esterified with geranylgeraniol. It also has a reduced cellular level of the light-harvesting LH2 complex, and the 850 nm absorbance maximum of LH2 is red-shifted by approximately 6 nm. Upon heterologous expression of the Synechocystis bchP homologue, not only are hydrogenated forms of bchlaGG detectable, but the level of LH2 is increased and the red-shift reversed by several nm. We conclude that this gene, which we term chlP, encodes the enzyme catalysing the stepwise hydrogenation of geranylgeraniol to phytol during chla biosynthesis.

Structural determination of dihydro‐ and tetrahydrogeranylgeranyl groups at the 17‐propionate of bacteriochlorophylls‐a

“…1) possessing a carboxy group at the 17 2 -position are esterified with various long hydrocarbon chains [4][5][6]. In oxygenic phototrophs, chlorophyllide-a is esterified with geranylgeranyl (GG) diphosphate by a Chl synthase (ChlG) to give geranylgeranylated Chl-a, and successive hydrogenation of three of its four C‚C double bonds by a GG reductase (ChlP) yields phytylated Chl-a via the intermediates possessing a dihydrogeranylgeranyl (DHGG) 1 and tetrahydrogeranylgeranyl (THGG) 1 ester (see Scheme 1).…”

“…In anoxygenic photosynthetic bacteria [4,5], it has been believed that reduction of a GG group occurred in the same manner as during Chl-a biosynthesis (vide supra). From some batch cultures of purple photosynthetic bacteria, BChls-a esterified with a GG, DHGG or THGG group in addition to major phytylated BChl-a were detected in at most 4% of total BChl-a component by HPLC [6,8,9]. However, the molecular structures of the DHGG-and THGG-type components have not been fully determined: these esters were only speculated on the basis of GC-MS analysis of their cleaved alcohols [8], but the positions of C‚C double bonds have not been confirmed in either of the esters.…”

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

“…The loss of the double bond at position 2 of GGPP prevents the formation of the allylic carbocation that accompanies the detachment of the diphosphate-leaving group, thereby rendering the reactions catalyzed by prenyltransferases impossible (14,15). Interestingly, archaeal GGRs are homologues of plant and bacterial GGRs, which specifically reduce three of the four double bonds in the geranylgeranyl side chain of chlorophyll or bacteriochlorophyll, yielding phytyl groups (1)(2)(3)12). GGR from Arabidopsis thaliana can also reduce GGPP to phytyl diphosphate, which retains the allylic double bond and is a substrate for prenyltransferases (12).…”

Menaquinone-Specific Prenyl Reductase from the Hyperthermophilic Archaeon Archaeoglobus fulgidus

“…During the past several years, the genes responsible for the reductive conversion of a geranylgeranyl group into a phytyl group have been identified in some higher plants and bacteria. The chlP genes from plants (12,17) and cyanobacteria (1) encode multifunctional geranylgeranyl reductase (GGR), which is involved in the biosyntheses of chlorophyll, tocopherol, and probably phyloquinone, whereas the bacterial homologue gene, bchP, encodes an enzyme that catalyzes the saturation of the geranylgeranyl moiety in bacteriochlorophyll and/or bacteriopheophytin (2,3). The amino acid sequences of these reductases have a high similarity with those of FAD/ NAD(P)H-dependent oxidoreductases, and these coenzymes have been shown to be sufficient for the activity of GGR from Arabidopsis thaliana (12).…”