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Abstract

Prenyltransferases (prenyl diphosphate synthases), which are a broad group of enzymes that catalyze the consecutive condensation of homoallylic diphosphate of isopentenyl diphosphates (IPP, C5) with allylic diphosphates to synthesize prenyl diphosphates of various chain lengths, have highly conserved regions in their amino acid sequences. Based on the above information, three prenyltransferase homologue genes were cloned from a thermophilic cyanobacterium, Synechococcus elongatus. Through analyses of the reaction products of the enzymes encoded by these genes, it was revealed that one encodes a thermolabile geranylgeranyl (C20) diphosphate synthase, another encodes a farnesyl (C15) diphosphate synthase whose optimal reaction temperature is 60 degrees C, and the third one encodes a prenyltransferase whose optimal reaction temperature is 75 degrees C. The last enzyme could catalyze the synthesis of five prenyl diphosphates of farnesyl, geranylgeranyl, geranylfarnesyl (C25), hexaprenyl (C30), and heptaprenyl (C35) diphosphates from dimethylallyl (C5) diphosphate, geranyl (C10) diphosphate, or farnesyl diphosphate as the allylic substrates. The product specificity of this novel kind of enzyme varied according to the ratio of the allylic and homoallylic substrates. The situations of these three S. elongatus enzymes in a phylogenetic tree of prenyltransferases are discussed in comparison with a mesophilic cyanobacterium of Synechocystis PCC6803, whose complete genome has been reported by Kaneko et al. (1996).

Chlorophyll a with a farnesyl tail in thermophilic cyanobacteria

“…These results support the hypothesis that the FPP synthase gene unique to T. elongatus (Ohto et al 1999) may enrich the pool of FPP enough for Chl a F synthesis in vivo . FPP would also serve as a precursor for other compounds to aid the cell in adapting to deal with higher temperatures such as by altering the rigidity of the lipid membrane.…”

“…With the abrupt truncation of a full isoprene unit, the electron density for this Chl a is unlikely to be the product of a gradually increasing B-factor along the tail due to its atomic mobility; rather it reveals a possible physiological relevance. As described above, a close examination of the literature regarding chlorophyll synthase activity (Rüdiger et al 1980) and FPP production in T. elongatus (Ohto et al 1999) reveals a plausible correlation between the biosynthetic pathway for chlorophyll a with a 15 carbon farnesyl tail and what has been observed here.…”

“…To confirm that the Chl a F compound could indeed be produced from the biochemical pathway described above, in which the tail precursor FPP is synthesized by a FPP synthase unique to T. elongatus with an optimal activity at 60 °C (Ohto et al 1999), we examined the correlation of Chl a F with growth temperature. We examined growth temperatures from 45 °C to 60 °C by studying pigment extracts from whole cells and purified PSII from T. elongatus (Figure 4).…”

“…In mesophilic cyanobacteria, FPP is not available within the cell to be used as a substrate by ChlG. However, specifically in the thermophilic cyanobacterium, T. elongatus , studies have previously identified a novel gene (named SelFPS) in the isoprenyl transferase family that specifically produces FPP optimally at 50–60 °C which is the optimal growth temperature range of T. elongates (Ohto et al 1999). We hypothesize that the presence of this SelFPS would enrich the cell in this precursor FPP and allow FPP to be utilized by ChlG as a substrate during Chl a biosynthesis.…”

Carotenoids in Algae: Distributions, Biosyntheses and Functions

“…This pathway has been confirmed by cloning genes from two species of Rhodobacter (purple bacteria) and two species of Pantoea (previously Erwinia ) [57–59]. Among oxygenic phototrophs, the functions of CrtE of Thermosynechococcus elongatus BP-1 [21], and CrtB of three species of cyanobacteria [22–24] and two species of green algae [25,26] have also been confirmed (Table 2). The crtE and crtB genes have high sequence similarity from bacteria to land plants, respectively.…”