Evaluation of multiple fused partners on enhancing soluble level of prenyltransferase NovQ in Escherichia coli.

To obtain the soluble production of recombinant NovQ, it has been constructed into the pET28a system. Unfortunately, NovQ was mostly accumulated as inclusion bodies and existed in insoluble fractions of E. coli cell lysate. Four partners, namely His6, TrxA, GST and MBP, were investigated in fusion expression and co-expression to achieve soluble expression in E. coli strains BL21 (DE3) and Rosetta™ (DE3). MBP fusion expression revealed a forceful function in enhancing solubility compared with others, in which the soluble protein was approximately 70% of the total cellular proteins in E. coli. Improvement of rare tRNA abundance promoted the yield of total recombinant protein and the expression level of soluble protein. Besides, one-step purification method was applied and the purity of recombinant protein obtained using Ni-NTA resin was over 90%, where soluble recombinant MBP-NovQ was cleaved using TEV protease in vitro. This method could be an ideal method for soluble expression of ABBA prenyltransferases in E. coli.

Production of Enzymes from Marine Actinobacteria.

Marine actinobacteria are well recognized for their capabilities to produce valuable natural products, which have great potential for applications in medical, agricultural, and fine chemical industries. In addition to producing unique enzymes responsible for biosynthesis of natural products, many marine actinobacteria also produce hydrolytic enzymes which are able to degrade various biopolymers, such as cellulose, xylan, and chitin. These enzymes are important to produce biofuels and biochemicals of interest from renewable biomass. In this chapter, the recent reports of novel enzymes produced by marine actinobacteria are reviewed, and advanced technologies that can be applied to search for novel marine enzymes as well as for improved enzyme production by marine actinobacteria are summarized, which include ribosome engineering, genome mining, as well as synthetic biology studies.

Expression, purification, crystallization and crystallographic study of the Aspergillus terreus aromatic prenyltransferase AtaPT.

Prenylated aromatics are produced by aromatic prenyltransferases during the secondary metabolism of bacteria, fungi and plants. The prenylation of nonprenylated precursors can lead to great chemical diversity and extensive biological properties. Aspergillus terreus aromatic prenyltransferase (AtaPT), which has recently been discovered and characterized, is such an enzyme and is responsible for the prenylation of various aromatic compounds. Here, recombinant AtaPT was overexpressed in Escherichia coli, purified and crystallized. Diffraction data were collected to a resolution of 1.71 Šand the crystal belonged to space group P2(1)2(1)2, with unit-cell parameters a = 96.2, b = 135.8, c = 69.5 Å, α = ß = γ = 90°. Analysis of the calculated Matthews coefficient and the self-rotation function suggested that there are two AtaPT molecules in the asymmetric unit.

A fungal prenyltransferase catalyzes the regular di-prenylation at positions 20 and 21 of paxilline.

A putative indole diterpene biosynthetic gene cluster composed of eight genes was identified in a genome database of Phomopsis amygdali, and from it, biosynthetic genes of fusicoccin A were cloned and characterized. The six genes showed significant similarities to pax genes, which are essential to paxilline biosynthesis in Penicillium paxilli. Recombinants of the three putative prenyltransferase genes in the cluster were overexpressed in Escherichia coli and characterized by means of in vitro experiments. AmyG is perhaps a GGDP synthase. AmyC and AmyD were confirmed to be prenyltransferases catalyzing the transfer of GGDP to IGP and a regular di-prenylation at positions 20 and 21 of paxilline, respectively. AmyD is the first know example of an enzyme with this function. The Km values for AmyD were calculated to be 7.6 ± 0.5 µM for paxilline and 17.9 ± 1.7 µM for DMAPP at a kcat of 0.12 ± 0.003/s.

GGPPS1 predicts the biological character of hepatocellular carcinoma in patients with cirrhosis.

BACKGROUND: Hepatocellular carcinoma (HCC) has been associated with diabetes and obesity, but a possible connection with the metabolic syndrome (MetS) and its potential interaction with hepatitis and cirrhosis are open to discussion. Our previous investigations have shown that GGPPS1 plays a critical role during hyperinsulinism. In this report, the expression and distribution of GGPPS1 in liver cancer, and its clinical significance were investigated. METHODS: 70 patients with hepatocellular carcinoma (HCC) were included in this study. Three different types of tissues from each HCC patient were assembled immediately after surgical resection: tumor-free tissue >5 cm far from tumor edge (TF), adjacent nonmalignant tissue within 2 cm (AT), and tissue from the tumor (TT). Normal liver tissues from 10 liver transplant donors served as healthy control (HC) while 10 patients with liver cirrhosis as cirrhosis control (CC). The expression and distribution of GGPPS1 were detected by immunohistochemistry, western blots, or real-time PCR. The relationship between the expression of GGPPS1 and clinic pathologic index were analyzed. RESULTS: We found that GGPPS1 was intensified mainly in the cytoplasm of liver tumor cells. Both the expression of GGPPS1 mRNA and protein were upregulated in TT comparing to AT or TF. Meanwhile, HCC patients with cirrhosis had relative higher expression of GGPPS1. In addition, many pathologic characters show close correlation with GGPPS1, such as tumor stage, vessel invasion, and early recurrence. CONCLUSION: GGPPS1 may play a critical role during the development of HCC from cirrhosis and is of clinical significance for predicting biological character of HCC.

The tumor suppressor TERE1 (UBIAD1) prenyltransferase regulates the elevated cholesterol phenotype in castration resistant prostate cancer by controlling a program of ligand dependent SXR target genes.

Castrate-Resistant Prostate Cancer (CRPC) is characterized by persistent androgen receptor-driven tumor growth in the apparent absence of systemic androgens. Current evidence suggests that CRPC cells can produce their own androgens from endogenous sterol precursors that act in an intracrine manner to stimulate tumor growth. The mechanisms by which CRPC cells become steroidogenic during tumor progression are not well defined. Herein we describe a novel link between the elevated cholesterol phenotype of CRPC and the TERE1 tumor suppressor protein, a prenyltransferase that synthesizes vitamin K-2, which is a potent endogenous ligand for the SXR nuclear hormone receptor. We show that 50% of primary and metastatic prostate cancer specimens exhibit a loss of TERE1 expression and we establish a correlation between TERE1 expression and cholesterol in the LnCaP-C81 steroidogenic cell model of the CRPC. LnCaP-C81 cells also lack TERE1 protein, and show elevated cholesterol synthetic rates, higher steady state levels of cholesterol, and increased expression of enzymes in the de novo cholesterol biosynthetic pathways than the non-steroidogenic prostate cancer cells. C81 cells also show decreased expression of the SXR nuclear hormone receptor and a panel of directly regulated SXR target genes that govern cholesterol efflux and steroid catabolism. Thus, a combination of increased synthesis, along with decreased efflux and catabolism likely underlies the CRPC phenotype: SXR might coordinately regulate this phenotype. Moreover, TERE1 controls synthesis of vitamin K-2, which is a potent endogenous ligand for SXR activation, strongly suggesting a link between TERE1 levels, K-2 synthesis and SXR target gene regulation. We demonstrate that following ectopic TERE1 expression or induction of endogenous TERE1, the elevated cholesterol levels in C81 cells are reduced. Moreover, reconstitution of TERE1 expression in C81 cells reactivates SXR and switches on a suite of SXR target genes that coordinately promote both cholesterol efflux and androgen catabolism. Thus, loss of TERE1 during tumor progression reduces K-2 levels resulting in reduced transcription of SXR target genes. We propose that TERE1 controls the CPRC phenotype by regulating the endogenous levels of Vitamin K-2 and hence the transcriptional control of a suite of steroidogenic genes via the SXR receptor. These data implicate the TERE1 protein as a previously unrecognized link affecting cholesterol and androgen accumulation that could govern acquisition of the CRPC phenotype.

Ectopic expression of the TERE1 (UBIAD1) protein inhibits growth of renal clear cell carcinoma cells: altered metabolic phenotype associated with reactive oxygen species, nitric oxide and SXR target genes involved in cholesterol and lipid metabolism.

Current studies of the TERE1 (UBIAD1) protein emphasize its multifactorial influence on the cell, in part due to its broad sub-cellular distribution to mitochondria, endoplasmic reticulum and golgi. However, the profound effects of TERE1 relate to its prenyltransferase activity for synthesis of the bioactive quinones menaquinone and COQ10. Menaquinone (aka, vitamin K-2) serves multiple roles: as a carrier in mitochondrial electron transport, as a ligand for SXR nuclear hormone receptor activation, as a redox modulator, and as an alkylator of cellular targets. We initially described the TERE1 (UBIAD1) protein as a tumor suppressor based upon reduced expression in urological cancer specimens and the inhibition of growth of tumor cell lines/xenografts upon ectopic expression. To extend this potential tumor suppressor role for the TERE1 protein to renal cell carcinoma (RCC), we applied TERE1 immunohistochemistry to a TMA panel of 28 RCC lesions and determined that in 57% of RCC lesions, TERE1 expression was reduced (36%) or absent (21%). Ectopic TERE1 expression caused an 80% decrease in growth of Caki-1 and Caki-2 cell lines, a significantly decreased colony formation, and increased caspase 3/7 activity in a panel of RCC cell lines. Furthermore, TERE1 expression increased mitochondrial oxygen consumption and hydrogen production, oxidative stress and NO production. Based on the elevated cholesterol and altered metabolic phenotype of RCC, we also examined the effects of TERE1 and the interacting protein TBL2 on cellular cholesterol. Ectopic TERE1 or TBL2 expression in Caki-1, Caki-2 and HEK 293 cells reduced cholesterol by up to 40%. RT-PCR analysis determined that TERE1 activated several SXR targets known to regulate lipid metabolism, consistent with predictions based on its role in menaquinone synthesis. Loss of TERE1 may contribute to the altered lipid metabolic phenotype associated with progression in RCC via an uncoupling of ROS/RNS and SXR signaling from apoptosis by elevation of cholesterol.

[Research progress in aromatic prenyltransferases originated from microorganisms].

The prenylation of aromatic compounds plays an important role in the natural product research because it not only gives rise to an astounding diversity of primary and secondary metabolites in plants, fungi and bacteria but also enhances the bioactivities and bioavailabilities of these compounds. However, further investigation of prenylated aromatic compounds is frequently hindered due to their low content in nature and difficulties in chemical synthesis. Cloning aromatic prenyltransferase genes followed by heterologous expression would be attractive tools for the chemoenzymatic synthesis of bioactive molecules. This review summarizes the classifications, structural investigations, enzymatic catalysis and other progress in aromatic prenyltransferases originated from microorganisms.

Identification of the verruculogen prenyltransferase FtmPT3 by a combination of chemical, bioinformatic and biochemical approaches.

Previous studies showed that verruculogen is the end product of a biosynthetic gene cluster for fumitremorgin-type alkaloids in Aspergillus fumigatus and Neosartorya fischeri. In this study, we isolated fumitremorgin A from N. fischeri. This led to the identification of the responsible gene, ftmPT3, for O-prenylation of an aliphatic hydroxy group in verruculogen. This gene was found at a different location in the genome of N. fischeri than the identified cluster. The coding sequence of ftmPT3 was amplified by fusion PCR and overexpressed in Escherichia coli. The enzyme product of the soluble His(8)-FtmPT3 with verruculogen and dimethylallyl diphosphate (DMAPP) was identified unequivocally as fumitremorgin A by NMR and MS analyses. K(M) values of FtmPT3 were determined for verruculogen and DMAPP at 5.7 and 61.5 µM, respectively. Average turnover number (k(cat)) was calculated from kinetic parameters of verruculogen and DMAPP to be 0.069 s(-1). FtmPT3 also accepted biosynthetic precursors of fumitremorgin A, for example, fumitremorgin B and 12,13-dihydroxyfumitremorgin C, as substrates and catalyses their prenylation.

Identification of bottlenecks in Escherichia coli engineered for the production of CoQ(10).

In this work, Escherichia coli was engineered to produce a medically valuable cofactor, coenzyme Q(10) (CoQ(10)), by removing the endogenous octaprenyl diphosphate synthase gene and functionally replacing it with a decaprenyl diphosphate synthase gene from Sphingomonas baekryungensis. In addition, by over-expressing genes coding for rate-limiting enzymes of the aromatic pathway, biosynthesis of the CoQ(10) precursor para-hydroxybenzoate (PHB) was increased. The production of isoprenoid precursors of CoQ(10) was also improved by the heterologous expression of a synthetic mevalonate operon, which permits the conversion of exogenously supplied mevalonate to farnesyl diphosphate. The over-expression of these precursors in the CoQ(10)-producing E. coli strain resulted in an increase in CoQ(10) content, as well as in the accumulation of an intermediate of the ubiquinone pathway, decaprenylphenol (10P-Ph). In addition, the over-expression of a PHB decaprenyl transferase (UbiA) encoded by a gene from Erythrobacter sp. NAP1 was introduced to direct the flux of DPP and PHB towards the ubiquinone pathway. This further increased CoQ(10) content in engineered E. coli, but decreased the accumulation of 10P-Ph. Finally, we report that the combined over-production of isoprenoid precursors and over-expression of UbiA results in the decaprenylation of para-aminobenzoate, a biosynthetic precursor of folate, which is structurally similar to PHB.

Defect in dolichol-dependent glycosylation increases sensitivity of Saccharomyces cerevisiae towards anti-fungal drugs.

Two temperature-sensitive Saccharomyces cerevisiae mutants, sec59-1 and dpm1-6, impaired, respectively, in dolichol kinase (Sec59p) and dolichyl phosphate mannose (DolPMan) synthase (Dpm1p), have an aberrant cell wall structure and composition. We tested their sensitivity to four classes of antifungal drugs used in clinical practice: 5-fluorocytosine, amphotericin B, caspofungin and itraconasole. The strains were resistant to itraconazole and sensitive to the other drugs used. The minimal inhibitory concentration (MIC) of caspofungin and amphotericin B was two-fold lower for sec59-1 and dpm1-6 than for the respective wild-type strains. The sensitivity of both mutants could be brought back to the wild-type level by a multicopy suppressor of the thermosensitive phenotype, the RER2 gene, encoding cis-prenyltransferase involved in dolichol biosynthesis. Biochemical analysis revealed slight changes of the cell wall composition, different in the mutants as compared to the wild-type in response to the drugs. Our data strongly support a relationship between dolichol phosphate level, protein glycosylation and antifungal sensitivity.

Simultaneous C7- and N1-prenylation of cyclo-L-Trp-L-Trp catalyzed by a prenyltransferase from Aspergillus oryzae.

A putative prenyltransferase gene cTrpPT was amplified from Aspergillus oryzae DSM1147, cloned into pQE70 and overexpressed in Escherichia coli. The overproduced His(6)-CTrpPT was purified to near homogeneity and incubated with L-tryptophan or tryptophan-containing cyclic dipeptides in the presence of dimethylallyl diphosphate. The formation of the enzyme products was monitored with HPLC. It was shown that CTrpPT differed clearly from other known indole prenyltransferases in several aspects. This enzyme showed higher substrate specificity towards aromatic substrates, but lower regioselectivity regarding the prenylation position than other indole prenyltransferases. Cyclo-L-Trp-L-Trp was much better accepted than other cyclic dipeptides tested in this study. In comparison to other indole prenyltransferases with one dominant enzyme product, at least two product peaks were detected in the reaction mixtures of CTrpPT. (1)H- and (13)C-NMR analyses, including long-range (1)H-(13)C connectivities in Heteronuclear Multiple-Bond Correlation (HMBC) and Nuclear Overhauser Effect Spectroscopy (NOESY), proved the structures of the enzyme products as C7- and N1-prenylated derivatives with a ratio of 1:1.2 using cyclo-L-Trp-L-Trp as substrate. The K(M) values were determined at about 2.5 mM for dimethylallyl diphosphate and 0.3 mM for cyclo-L-Trp-L-Trp with a turnover number of 0.33 s(-1).

Preparation of pyrrolo[2,3-b]indoles carrying a beta-configured reverse C3-dimethylallyl moiety by using a recombinant prenyltransferase CdpC3PT.

Six beta-configured reversely C3-prenylated pyrrolo[2,3-b]indoles were successfully prepared by using a recombinant prenyltransferase from Neosartorya fischeri. For this purpose, the putative prenyltransferase gene NFIA_074280 (termed herewith cdpC3PT) was cloned into pQE60 and overexpressed in Escherichia coli. The overproduced His(6)-CdpC3PT was purified to near homogeneity and incubated with five cyclic tryptophan-containing dipeptides in the presence of dimethylallyl diphosphate (DMAPP). All of the substrates were accepted by CdpC3PT and converted to reversely C3-prenylated pyrrolo[2,3-b]indoles. Using cyclo-l-Trp-l-Trp as substrate, both mono- and diprenylated derivatives were obtained. The structures of the enzymatic products were confirmed by HR-ESI-MS, (1)H- and (13)C-NMR analyses as well as by long-range (1)H-(13)C connectivities in heteronuclear multiple-bond correlation (HMBC) spectra after preparative isolation. (1)H-(1)H spatial correlations in nuclear overhauser effect spectroscopy (NOESY) were used for determination of absolute configuration. The K(M) values were determined at about 1.5 mM for DMAPP and in the range from 0.22 to 5.5 mM for cyclic dipeptides. The turnover number k(cat) were found in the range of 0.023 to 0.098 s(-1) and specificity constants k(cat)/K(M) from 14.2 to 122.7 M(-1) s(-1). In contrast to the products of AnaPT bearing alpha-configured C3-dimethylallyl residues, the C3-prenyl moieties in the products of CdpC3PT have a beta-configuration. Discovery and characterisation of CdpC3PT expand the usage of the chemoenzymatic approach for stereospecific synthesis of C3-prenylated derivatives.

NovQ is a prenyltransferase capable of catalyzing the addition of a dimethylallyl group to both phenylpropanoids and flavonoids.

NovQ is a member of a recently identified CloQ/NphB class of prenyltransferases. Although NphB has been well characterized as a prenyltransferase with flexibility against aromatic substrates, few studies have been carried out on characterization of NovQ. Hence, in this study, we investigate the kinetics, substrate specificity and regiospecificity of NovQ. The corresponding novQ gene was cloned from Streptomyces niveus, which produces an aminocoumarin antibiotic, novobiocin. Recombinant NovQ was overexpressed in Escherichia coli and purified to homogeneity. The purified enzyme was a soluble monomeric 40-kDa protein that catalyzed the transfer of a dimethylallyl group to 4-hydroxyphenylpyruvate (4-HPP) independently of divalent cations to yield 3-dimethylallyl-4-HPP, an intermediate of novobiocin. Steady-state kinetic constants for NovQ with the two substrates, 4-HPP and dimethylallyl diphosphate, were also calculated. In addition to the prenylation of 4-HPP, NovQ catalyzed carbon-carbon-based and carbon-oxygen-based prenylations of a diverse collection of phenylpropanoids, flavonoids and dihydroxynaphthalenes. Despite its catalytic promiscuity, the NovQ-catalyzed prenylation occurred in a regiospecific manner. NovQ is the first reported prenyltransferase capable of catalyzing the transfer of a dimethylallyl group to both phenylpropanoids, such as p-coumaric acid and caffeic acid, and the B-ring of flavonoids. This study shows that NovQ can serve as a useful biocatalyst for the synthesis of prenylated phenylpropanoids and prenylated flavonoids.

Prenylation of flavonoids by biotransformation of yeast expressing plant membrane-bound prenyltransferase SfN8DT-1.

Prenylated flavonoids are natural products that exhibit diverse biological effects and often represent the active components of various medicinal plants. This study demonstrated the production of prenylated naringenin by biotransformation using transgenic yeast expressing naringenin 8-dimethylallyltransferase, a membrane-bound enzyme, without feeding of prenyl donors. This method provides the possibility of generating prenylated flavonoids that occur rarely in nature.

Overexpression of the Saccharomyces cerevisiae RER2 gene in Trichoderma reesei affects dolichol dependent enzymes and protein glycosylation.

Protein secretion in Trichoderma reesei could be stimulated by overexpression of the yeast Saccharomyces cerevisiae DPM1 gene encoding dolichyl phosphate mannose synthase (DPMS) a key enzyme in the O-glycosylation pathway. The secreted proteins were glycosylated to the wild type level. On the other hand, the elevated concentration of GDP-mannose, a direct substrate for DPMS, resulting from overexpression in T. reesei of the mpg1 gene coding for guanyltransferase, did not affect secretion of proteins but did affect the degree of their O- and N-glycosylation. In this paper, we examined the effects of dolichol, an indispensable carrier of sugar residues in protein glycosylation, on the synthesis of glycosylated proteins. An increase in dolichol synthesis was obtained by overexpression of the yeast gene encoding cis-prenyltransferase, the first enzyme of the mevalonate pathway committed to dolichol biosynthesis. We observed that, an increased concentration of dolichol resulted in an increased expression of the dpm1 gene and DPMS activity and in overglycosylation of secreted proteins.

Cloning and characterization of farnesyl diphosphate synthase from the rubber-producing mushroom Lactarius chrysorrheus.

Farnesyl diphosphate is involved in rubber biosynthesis as an initiating substrate for both polyprenol and mushroom rubber. So far, we have isolated the cDNA of a farnesyl diphosphate synthase (FPS) for the first time from a rare rubber-producing mushroom, Lactarius chrysorrheus, by the degenerate RT-PCR technique based on sequence information of FPS genes from fungi and yeasts. The open reading frame was clarified to encode a protein of 381 amino acid residues with a calculated molecular weight of 42.9 kDa. The deduced amino acid sequence of L. chrysorrheus FPS showed about 50% identity with those of other fungi and yeasts as well as plants. We expressed the cDNA of L. chrysorrheus FPS in Escherichia coli as a glutathione-S-transferase (GST)-fusion protein. The purified obtained protein showed FPS activity in which geranyl diphosphate (GPP) served as primary substrate, with a 2.4-fold higher k(cat)/K(m) value for GPP than for dimethylallyl diphosphate (DMAPP).

Transcriptional regulation of farnesyl pyrophosphate synthase by liver X receptors.

Liver X receptors (LXRs) are members of the nuclear receptor superfamily that are involved in cholesterol and lipid metabolism. In addition to liver, the brain is another site where LXRs may control cholesterol homeostasis. In the brain, the regulation of cholesterol homeostasis is independent from other parts of the body, and its disturbance is associated with neurodegenerative disorders, such as Alzheimer's disease. We have used PCR-based suppressive subtractive cloning to identify new LXR target genes in brain cells. In this report, we show that farnesyl pyrophosphate synthase (FPPS) is a new target gene for LXR in astrocytes and neurons. Farnesyl pyrophosphate is an obligate intermediate for de novo cholesterol synthesis and a substrate for protein farnesylation. Stimulation of FPPS mRNA synthesis by an LXR agonist, Hypocholamide, was observed in several cell lines from the central nervous system. We identified a single putative direct repeat 4 (DR4) LXR response element in the FPPS promoter. In a reporter gene assay, LXR transactivated a reporter gene bearing a truncated FPPS promoter containing this DR4 cis-element but not if the DR4 element was mutated. Using gel-mobility shift assay, we further demonstrated the direct interaction between the LXR/retinoid X receptor (RXR) heterodimer and the response element. Taken together, our results indicate that LXRs directly regulate FPPS gene expression, and thus may play a role in modulating cholesterol synthesis in the brain.

Yeast Saccharomyces cerevisiae has two cis-prenyltransferases with different properties and localizations. Implication for their distinct physiological roles in dolichol synthesis.

BACKGROUND: Dolichol is a family of long-chain polyprenols, which is utilized as a sugar carrier in protein glycosylation in the endoplasmic reticulum (ER). We have identified a key enzyme of the dolichol synthesis, cis-prenyltransferase, as Rer2p from Saccharomyces cerevisiae. We have also isolated a multicopy suppressor of an rer2 mutant and named it SRT1. It encodes a protein similar to Rer2p but its function has not been established. RESULTS: The cis-prenyltransferase activity of Srt1p has been proved biochemically in the lysate of yeast cells lacking Rer2p. The polyprenol product of Srt1p is longer in chain length than that of Rer2p and is not sufficiently converted to dolichol and dolichyl phosphate, unlike that of Rer2p. The subcellular localization of these two isozymes has been examined by immunofluorescence microscopy and by the use of GFP fusion proteins. Whereas GFP-Rer2p is localized to the continuous ER and some dots associated with the ER, GFP-Srt1p shows only punctate localization patterns. Immunofluorescence double staining with Erg6p, a marker of lipid particles in yeast, indicates that Srt1p is mainly localized to lipid particles (lipid bodies). RER2 is mainly expressed in the early logarithmic phase, while the expression of SRT1 is induced in the stationary phase. CONCLUSIONS: We have shown that yeast has two active cis-prenyltransferases with different properties. This result implies that the two isozymes have different physiological roles during the life cycle of the yeast.

Chain length determination of prenyltransferases: both heteromeric subunits of medium-chain (E)-prenyl diphosphate synthase are involved in the product chain length determination.

Among prenyltransferases, medium-chain (E)-prenyl diphosphate synthases are unusual because of their heterodimeric structures. The larger subunit has highly conserved regions typical of (E)-prenyltransferases. The smaller one has recently been shown to be involved in the binding of allylic substrate as well as determining the chain length of the reaction product [Zhang, Y.-W., et al. (1999) Biochemistry 38, 14638-14643]. To better understand the product chain length determination mechanism of these enzymes, several amino acid residues in the larger subunits of Micrococcus luteus B-P 26 hexaprenyl diphosphate synthase and Bacillus subtilis heptaprenyl diphosphate synthase were selected for substitutions by site-directed mutagenesis and examined by combination with the corresponding wild-type or mutated smaller subunits. Replacement of the Ala at the fifth position upstream to the first Asp-rich motif with bulky amino acids in both larger subunits resulted in shortening the chain lengths of the major products, and a double combination of mutant subunits of the heptaprenyl diphosphate synthase, I-D97A/II-A79F, yielded exclusively geranylgeranyl diphosphate. However, the combination of a mutant subunit and the wild-type, I-Y103S/II-WT or I-WT/II-I76G, produced a C(40) prenyl diphosphate, and the double combination of the mutants, I-Y103S/II-I76G, gave a reaction product with longer prenyl chain up to C(50). These results suggest that medium-chain (E)-prenyl diphosphate synthases take a novel mode for the product chain length determination, in which both subunits cooperatively participate in maintaining and determining the product specificity of each enzyme.