Cytoplasmic Escherichia coli ADP sugar pyrophosphatase binds to cell membranes in response to extracellular signals as the cell population density increases

ADP sugar pyrophosphatase (AspP) is a member of the 'Nudix' (Nucleoside diphosphate linked to some other moiety X) hydrolase family of enzymes that catalyzes the hydrolytic breakdown of ADP-glucose (ADPG) linked to glycogen biosynthesis. In a previous work, we showed that AspP activity is strongly enhanced by both glucose-1,6-bisphosphate and nucleotide-sugars, and by macromolecular crowding. In this work, we show that AspP binds to cell membranes as the bacterial population density increases, c. 30% of the total enzyme remaining membrane associated as glycogen depletes during the stationary phase. This process is not dependent on the stationary transcription factor RpoS, the producer of the bacterial quorum-sensing autoinducer 2 (LuxS), the presence of glycogen granules or glucose availability, but is stimulated by small soluble heat-labile molecule(s) occurring in cell-free spent supernatants of stationary cultures that are acid stabile and base labile. These data further point to AspP as a highly regulated enzyme, and provide a first set of evidences indicating that glycogen metabolism is subjected to regulation by intercellular communication in Escherichia coli.

Escherichia coli AspP activity is enhanced by macromolecular crowding and by both glucose-1,6-bisphosphate and nucleotide-sugars

Escherichia coli ADP-sugar pyrophosphatase (AspP) is a "Nudix" hydrolase that catalyzes the hydrolytic breakdown of ADP-glucose linked to glycogen biosynthesis. Moderate increases of AspP activity in the cell are accompanied by significant reductions of the glycogen content. In vitro analyses showed that AspP activity is strongly enhanced by macromolecular crowding and by both glucose-1,6-bisphosphate and nucleotide-sugars, providing a first set of indicative evidences that AspP is a highly regulated enzyme. To our knowledge, AspP is the sole bacterial enzyme described to date which is activated by both G1,6P(2) and nucleotide-sugars.

Glycogen phosphorylase, the product of the glgP Gene, catalyzes glycogen breakdown by removing glucose units from the nonreducing ends in Escherichia coli

To understand the biological function of bacterial glycogen phosphorylase (GlgP), we have produced and characterized Escherichia coli cells with null or altered glgP expression. glgP deletion mutants (DeltaglgP) totally lacked glycogen phosphorylase activity, indicating that all the enzymatic activity is dependent upon the glgP product. Moderate increases of glycogen phosphorylase activity were accompanied by marked reductions of the intracellular glycogen levels in cells cultured in the presence of glucose. In turn, both glycogen content and rates of glycogen accumulation in DeltaglgP cells were severalfold higher than those of wild-type cells. These defects correlated with the presence of longer external chains in the polysaccharide accumulated by DeltaglgP cells. The overall results thus show that GlgP catalyzes glycogen breakdown and affects glycogen structure by removing glucose units from the polysaccharide outer chains in E. coli.

Sucrose synthase controls both intracellular ADP glucose levels and transitory starch biosynthesis in source leaves

The prevailing model on transitory starch biosynthesis in source leaves assumes that the plastidial ADPglucose (ADPG) pyrophosphorylase (AGP) is the sole enzyme catalyzing the synthesis of the starch precursor molecule, ADPG. However, recent investigations have shown that ADPG linked to starch biosynthesis accumulates outside the chloroplast, presumably in the cytosol. This finding is consistent with the occurrence of an 'alternative' gluconeogenic pathway wherein sucrose synthase (SuSy) is involved in the production of ADPG in the cytosol, whereas both plastidial phosphoglucomutase (pPGM) and AGP play a prime role in the scavenging of starch breakdown products. To test this hypothesis, we have compared the ADPG content in both Arabidopsis and potato wild-type (WT) leaves with those of the starch-deficient mutants with reduced pPGM and AGP. These analyses provided evidence against the 'classical' model of starch biosynthesis, since ADPG levels in all the starch-deficient lines were normal compared with WT plants. Whether or not SuSy is involved in the synthesis of ADPG accumulating in leaves was tested by characterizing both SuSy-overexpressing and SuSy-antisensed transgenic leaves. Importantly, SuSy-overexpressing leaves exhibited a large increase of both ADPG and starch levels compared with WT leaves, whereas SuSy-antisensed leaves accumulated low amounts of both ADPG and starch. These findings show that (i) ADPG produced by SuSy is linked to starch biosynthesis; (ii) SuSy exerts a strong control on the starch biosynthetic process; and (iii) SuSy, but not AGP, controls the production of ADPG accumulating in source leaves.

Most of ADP x glucose linked to starch biosynthesis occurs outside the chloroplast in source leaves

Sucrose and starch are end products of two segregated gluconeogenic pathways, and their production takes place in the cytosol and chloroplast of green leaves, respectively. According to this view, the plastidial ADP.glucose (ADPG) pyrophosphorylase (AGP) is the sole enzyme catalyzing the synthesis of the starch precursor molecule ADPG. However, a growing body of evidences indicates that starch formation involves the import of cytosolic ADPG to the chloroplast. This evidence is consistent with the idea that synthesis of the ADPG linked to starch biosynthesis takes place in the cytosol by means of sucrose synthase, whereas AGP channels the glucose units derived from the starch breakdown. To test this hypothesis, we first investigated the subcellular localization of ADPG. Toward this end, we constructed transgenic potato plants that expressed the ADPG-cleaving adenosine diphosphate sugar pyrophosphatase (ASPP) from Escherichia coli either in the chloroplast or in the cytosol. Source leaves from plants expressing ASPP in the chloroplast exhibited reduced starch and normal ADPG content as compared with control plants. Most importantly however, leaves from plants expressing ASPP in the cytosol showed a large reduction of the levels of both ADPG and starch, whereas hexose phosphates increased as compared with control plants. No pleiotropic changes in photosynthetic parameters and maximum catalytic activities of enzymes closely linked to starch and sucrose metabolism could be detected in the leaves expressing ASPP in the cytosol. The overall results show that, essentially similar to cereal endosperms, most of the ADPG linked to starch biosynthesis in source leaves occurs in the cytosol.

Alkali metal ions protect mitochondrial rhodanese against thermal inactivation

Incubation of bovine liver mitochondrial rhodanese in dilute, reducing solutions at temperatures ranging between 30 and 45 degreesC conduced to a rapid loss of enzymatic activity. This inactivation was substantially reduced in the presence of millimolar concentrations of alkali metal ions, divalent cations (including Mg2+, Ca2+, and Ba2+) were ineffective. The extent of protection afforded by monovalent cations was highly dependent on their ionic radii, with K+ and Na+ ions being the most effective protective agents. The protection afforded by a number of anions, including thiosulfate, could be totally ascribed to the presence of the accompanying monovalent cation. The overall results indicate that K+ and Na+, at concentrations and temperatures within the physiological range, substantially contribute to the stabilization of the functional structure of rhodanese.

Purification and characterization of Chromatium vinosum GroEL and GroES proteins overexpressed in Escherichia coli cells lacking the endogenous groESL operon

Using an Escherichia coli strain (RF101) in which the endogenous chromosomal groESL operon was removed, we overexpressed the GroEL and GroES chaperonins cloned from the photosynthetic bacterium Chromatium vinosum. The identities of these proteins were confirmed by immunological and N-terminal sequence analyses. The native molecular masses of GroEL and GroES, as determined by size-exclusion chromatography, were 830 and 74 kDa, respectively. This suggests a tetradecameric structure for GroEL and a heptameric structure for GroES. C. vinosum GroEL catalyzed a K+-stimulated ATP hydrolysis with a specific activity at 25 degreesC of 50.2 +/- 3.8 nmol Pi released min-1 mg protein-1. GroEL ATPase was inhibited by GroES, reaching about 50% inhibition at a ratio GroES-7mer/GroEL-14mer of 1 in the presence of 10 mM KCl. The ATPase Vmax increased almost fivefold in the 25 to 65 degreesC temperature range; higher temperatures led to a rapid inactivation of this activity. The chaperone activity of the C. vinosum GroEL/GroES system was characterized by its effect on the refolding of guanidinium chloride-unfolded rhodanese. In the presence of ATP and GroES, C. vinosum GroEL assisted rhodanese refolding. The heterologous combination C. vinosum GroEL/E. coli GroES or E. coli GroEL/C. vinosum GroES was as effective as the homologous complexes. In summary, this strategy allowed the purification at high yields of fully functional, homogenous C. vinosum GroEL and GroES chaperonins from E. coli.

Phosphorylation of an envelope-associated Hsp70 homolog in amyloplasts isolated from cultured cells of sycamore (Acer pseudoplatanus L.)

The presence of Hsp70 and Hsp60 molecular chaperones in amyloplasts isolated from cultured sycamore cells was analyzed by immunoblotting. Hsp70 homologs were located in both amyloplast envelope and stromal fractions, but no Hsp60 homologs were detected in any of the different suborganellar fractions. Incubation of whole amyloplasts or their envelope fraction with Mg2+ gamma-32P-ATP resulted in a rapid phosphorylation of the envelope-associated Hsp70 homolog, which constitutes a major target of phosphorylation in these plastids.

Genomic diversity among Streptococcus agalactiae isolates detected by a degenerate oligonucleotide-primed amplification assay

A random-amplified polymorphic DNA assay using partially degenerate oligonucleotides as primers was used for the characterization of 78 epidemiologically related and unrelated clinical isolates of Streptococcus agalactiae belonging to different serotypes. Thirty distinct amplification profiles were obtained among 52 unrelated S. agalactiae isolates assigned to nine groups by serotyping (including 3 nontypeable strains), uncovering the extent of genomic heterogeneity existent within serotypes. This method was particularly useful in providing evidence for or against vertical transmission of a given clone of this microorganism, as well as for relapsing or reinfection in related cases, and suggested clonal relatedness between unrelated S. agalactiae isolates associated with some invasive infections. Thus, this simple methodology represents a suitable tool for the epidemiologic study of S. agalactiae infections.

Cooperation of the DnaK and GroE chaperone systems in the folding pathway of plant ferredoxin-NADP+ reductase expressed in Escherichia coli

The DnaK system is required for the productive folding of pea chloroplast ferredoxin-NADP+ reductase (FNR) expressed in Escherichia coli. The formation of a mature active enzyme was severely impaired in E. coli dnaK, dnaJ or grpE mutants expressing either the cytosolic precursor of the reductase (preFNR) or the mature apoenzyme, and these forms aggregated extensively in these cells. Coexpression of dnaK from a multicopy plasmid in the dnaK-null mutants restored preFNR processing and folding of FNR, rendering a mature-sized active enzyme. Overexpression of GroESL chaperonins failed to prevent preFNR aggregation, but it restored productive folding of FNR in dnaK-null mutants expressing the mature enzyme. Expression of preFNR in OmpT-protease-deficient E. coli cells resulted in the accumulation of the unprocessed precursor in the soluble fraction of the cells. The interaction of this soluble preFNR, but not the mature reductase, with DnaK and GroEL was evidenced by immunoprecipitation studies. We conclude that, in addition to the GroE chaperonins [Carrillo, N., Ceccarelli, E. A., Krapp, A. R., Boggio, S., Ferreyra, R. G. & Viale, A. M. (1992) J. Biol. Chem. 267, 15537-15541], the DnaK chaperone system plays a crucial role in the folding pathway of FNR.

Isolation and characterization of a dnaK genomic locus in a halotolerant cyanobacterium Aphanothece halophytica

We cloned and characterized a genomic locus encoding a distinct member of the DnaK/Hsp70 family of molecular chaperones, dnaK1, from the halotolerant cyanobacterium Aphanothece halophytica. Co-expression of dnaK1 with a plant plastocyanin precursor in Escherichia coli resulted in a dramatic increase in the solubility of the plant protein. This indicates that A. halophytica dnaK1 encodes a functional protein possessing functions assigned to DnaK/Hsp70 chaperone members. The A. halophytica dnaK1 locus also encompasses grpE and dnaJ homologue genes in the order grpE-dnaK1-dnaJ. The transcript content of dnaK1 increased strongly upon subjecting cyanobacterial cells to heat stress. Northern analyses using specific probes indicated transcript species of 2.8, 2.2, 1.3, and 0.7 kb, which comprised grpE-dnaK1, dnaK1, dnaJ, and grpE, respectively. This indicates the presence of different terminators and/or heat stress promoters in this locus. Both dnaK1 transcript and protein levels increased in cyanobacterial cells transferred to hyperosmotic environments, suggesting a role of DnaK1 in the protection and/or recovery of A. halophytica from this particular stress.

The 70-kDa heat-shock protein/DnaK chaperone system is required for the productive folding of ribulose-biphosphate carboxylase subunits in Escherichia coli

We have studied the in vivo requirements of the DnaK chaperone system for the folding of recombinant ribulose-bisphosphate carboxylase/oxygenase in Escherichia coli. Expression of functional dimeric or hexadecameric ribulose-bisphosphate carboxylase from different bacterial sources (including purple bacteria and cyanobacteria) was severely impaired in E. coli dnaK, dnaJ, or grpE mutants. These enzymes were synthesized mostly in soluble, fully enzymatically active forms in wild-type E. coli cells cultured in the temperature range 20-42 degrees C, but aggregated extensively in dnaK null mutants. Co-expression of dnaK, but not groESL, markedly reduced the aggregation of ribulose-bisphosphate carboxylase subunits in dnaK null mutants and restored the enzyme activity to levels found in isogenic wild-type strains. Ribulose-bisphosphate carboxylase expression in wild-type E. coli cells growing at 30 degrees C promoted an enhanced synthesis of stress proteins, apparently by sequestering DnaK from its negative regulatory role in this response. The overall results indicate that the DnaK chaperone system assists in vivo the folding pathway of ribulose-bisphosphate carboxylase large subunits, most probably at its very early stages.

Evolutionary relationships among eubacterial groups as inferred from GroEL (chaperonin) sequence comparisons

The essential GroEL proteins represent a subset of molecular chaperones ubiquitously distributed among species of the eubacterial lineage, as well as in eukaryote organelles. We employed these highly conserved proteins to infer eubacterial phylogenies. GroEL from the species analyzed clustered in distinct groups in evolutionary trees drawn by either the distance or the parsimony method, which were in general agreement with those found by 16S rRNA comparisons (i.e., proteobacteria, chlamydiae, bacteroids, spirochetes, firmicutes [gram-positive bacteria], and cyanobacteria-chloroplasts). Moreover, the analysis indicated specific relationships between some of the aforementioned groups which appeared not to be clearly defined or controversial in rRNA-based phylogenetic studies. For instance, a monophyletic origin for the low-G+C and high-G+C subgroups among the firmicutes, as well as their specific relationship to the cyanobacteria-chloroplasts, was inferred. The general observations suggest that GroEL proteins provide valuable evolutionary tools for defining evolutionary relationships among the eubacterial lineage of life.

The chaperone connection to the origins of the eukaryotic organelles

The heat-shock 60 proteins (Hsp60) constitute a subset of molecular chaperones essential for the survival of the cell, present in eubacteria as well as in eukaryotic organelles. Here, we have employed these highly conserved proteins for the inferences of the origins of the organelles. Hsp60s present in mitochondria from different eukaryotic lineages formed a clade, which showed the closest relationship to that of the Ehrlichia/Rickettsia cluster among the alpha-Proteobacteria. This, in addition to phenotypic characteristics, suggests that these obligate intracellular parasites and the lineage that generated the mitochondrion shared last common ancestry. In turn, Hsp60s present in chloroplasts from plants and a red alga, respectively, clustered specifically with those of the cyanobacteria, suggesting that all plastids derive exclusively from this eubacterial lineage.

Cloning, characterization, and functional expression in Escherichia coli of chaperonin (groESL) genes from the phototrophic sulfur bacterium Chromatium vinosum

A recombinant lambda phage which was able to propagate in groE mutants of Escherichia coli was isolated from a Chromatium vinosum genomic DNA library. A 4-kbp SalI DNA fragment, isolated from this phage and subcloned in plasmid vectors, carried the C. vinosum genes that allowed lambda growth in these mutants. Sequencing of this fragment indicated the presence of two open reading frames encoding polypeptides of 97 and 544 amino acids, respectively, which showed high similarity to the molecular chaperones GroES and GroEL, respectively, from several eubacteria and eukaryotic organelles. Expression of the cloned C. vinosum groESL genes in E. coli was greatly enhanced when the cells were transferred to growth temperatures that induce the heat shock response in this host. Coexpression in E. coli of C. vinosum groESL genes and the cloned ribulose bisphosphate carboxylase/oxygenase genes from different phototrophic bacteria resulted in an enhanced assembly of the latter enzymes. These results indicate that the cloned DNA fragment encodes C. vinosum chaperonins, which serve in the assembly process of oligomeric proteins. Phylogenic analysis indicates a close relationship between C. vinosum chaperonins and their homologs present in pathogenic species of the gamma subdivision of the eubacterial division Proteobacteria.

Assembly of plant ferredoxin-NADP+ oxidoreductase in Escherichia coli requires GroE molecular chaperones

We have recently reported the expression in Escherichia coli of an enzymatically competent ferredoxin-NADP+ oxidoreductase from cloned pea genes encoding either the mature enzyme or its precursor protein (Ceccarelli, E. A., Viale, A. M., Krapp, A. R., and Carrillo, N. (1991) J. Biol. Chem. 266, 14283-14287). Processing to the mature form by bacterial protease(s) and FAD assembly occurred in the bacterial cytosol. Expression of ferredoxin-NADP+ reductase in chaperonin-deficient (groE-) mutants of E. coli resulted in partial reductase assembly at permissive growth temperatures (i.e. 30 degrees C), and in total breakdown of holoenzyme assembly, and accumulation as aggregated inclusion bodies at non-permissive temperatures (i.e. 42 degrees C). Coexpression in these mutants of a cloned groESL operon from the phototrophic bacterium Chromatium vinosum resulted in partial or total recoveries of ferredoxin-NADP+ reductase assembly. The overall results indicate that bacterial chaperonins are required for the productive folding/assembly of eucaryotic ferredoxin-NADP+ reductase expressed in E. coli.

Comparative analysis of mitochondrial and amyloplast adenylate translocators

Structurally intact and metabolically competent mitochondria isolated from liquid-culture cells of sycamore (Acer pseudoplatanus L.) were shown to incorporate ADPglucose. Employing the double silicone oil layer filtering centrifugation method, we examined the kinetic properties of the uptake of various adenylates as well as the inhibitory effects exerted by carboxyatractyloside, atractyloside and bongkrekic acid, known specific inhibitors of the mitochondrial adenylate translocator. Immunoblot patterns of peptides derived from the partial proteolytic digestion of the mitochondrial and plastid adenylate translocators were shown to be essentially the same. We conclude that the molecular entities engaged in the adenylate transport system operating in two different organelles, mitochondria and amyloplasts, are very similar.

Expression, assembly, and processing of an active plant ferredoxin-NADP+ oxidoreductase and its precursor protein in Escherichia coli

The flavoprotein ferredoxin-NADP+ reductase (FNR) catalyzes the final step of the photosynthetic electron transport chain, i.e. the reduction of NADP+ by ferredoxin. A cloned FNR cDNA from a pea library (Newman, B., and Gray, J. (1988) Plant Mol. Biol. 10, 511-520) was used to construct plasmids which express the apoenzyme in Escherichia coli. Two recombinant vectors were prepared, one containing the sequence corresponding to the mature enzyme and another including, in addition, the sequence of the transit peptide that directs FNR to the chloroplast. These proteins were expressed as fusion products to the NH2-terminal portion of beta-galactosidase. In both cases, a 35-kDa immunoreactive polypeptide was the major product, suggesting that the proteins were processed in vivo. NH2-terminal sequence determination of the purified recombinant proteins indicate cleavage at positions -1/-2 with respect to the normal processing site in chloroplasts. The processed enzymes showed enzymatic activities and spectral properties that were similar or identical to those of native plant FNR. When a La protease-deficient E. coli strain was used as a host, the expressed FNR precursor was found to be poorly processed, associated to bacterial pellets, and showed no detectable FNR activity. The overall results indicate that acquisition of the native enzyme conformation and assembly of the prosthetic group takes place in the bacterial host, generating an enzyme that is, as far as studied, indistinguishable from plant FNR.

rbcR [correction of rcbR], a gene coding for a member of the LysR family of transcriptional regulators, is located upstream of the expressed set of ribulose 1,5-bisphosphate carboxylase/oxygenase genes in the photosynthetic bacterium Chromatium vinosum

An open reading frame, rbcR, was identified 226 bp upstream of rbcAB, i.e., the ribulose 1,5-bisphosphate carboxylase genes expressed in the phototrophic purple bacterium Chromatium vinosum. Several features reveal that rbcR encodes a member of the LysR family of transcriptional regulators, in which an anomalous content of lysine and arginine residues (Lys/Arg anomaly) was found. The expression of rbcR in Escherichia coli as a protein fused to the N-terminal region of beta-galactosidase led to reduced expression of rbcAB. Thus, rbcR is likely to encode a trans-acting transcriptional regulator of rbcAB expression in C. vinosum.

Characterization and Intraorganellar Distribution of Protein Kinases in Amyloplasts Isolated from Cultured Cells of Sycamore (Acer pseudoplatanus L.)

Incubation of amyloplasts isolated from cultured cells of sycamore (Acer pseudoplatanus L.) with [gamma-(32)P]ATP resulted in the rapid phosphorylation (half-time of 40 seconds at 25 degrees Celcius) of organellar polypeptides. The preferred substrate for amyloplast protein kinases was Mg(2+). ATP, and recovery of only [(32)P]serine after partial acid hydrolysis indicated the predominance of protein serine kinases in the organelle. These activities were located in the envelope and stromal fractions of the plastid, which showed different specificities toward exogenous protein substrates and distinct patterns of phosphorylation of endogenous polypeptides. A 66-kilodalton polypeptide, inaccessible to an exogenously added protease, was one of the major phosphorylated products found in intact amyloplasts at low [gamma-(32)P] adenosine triphosphate concentrations. This polypeptide represented the major phosphoprotein observed with the isolated envelope fraction. The patterns of polypeptide phosphorylation found in intact amyloplasts and chloroplasts from cultured cell lines of sycamore were clearly distinguishable. The overall results indicate the presence of protein phosphorylation systems unique to this reserve plastid present in nonphotosynthetic tissues.

Direct transport of ADPglucose by an adenylate translocator is linked to starch biosynthesis in amyloplasts

Starch biosynthesis has been studied by using amyloplasts isolated from cultured cells of sycamore trees (Acer pseudoplatanus L.). Highly purified intact amyloplasts, free from mitochondria and starch granules derived from broken amyloplasts, were isolated from a Percoll step gradient. Subsequently, the double silicone oil layer centrifugation technique was used to study adenylate transport in the amyloplasts. An adenylate-specific carrier was found to be active in the uptake of ATP, ADP, AMP, and most importantly, ADPglucose (ADP-Glc). Kinetic analyses showed that the uptake of these adenylates was mutually competitive with each other. In contrast to the mitochondrial adenylate carrier, in amyloplasts only ATP and ADP-Glc uptake were inhibited by carboxyatractyloside. Evidence is presented that the ADP-Glc transported into the amyloplast stroma can be used in starch synthesis catalyzed by starch synthase (ADP-Glc:1,4-alpha-D-glucan 4-alpha-D-glucosyltransferase, EC 2.4.1.21). We propose that starch biosynthesis in amyloplasts is tightly coupled with the direct transport of ADP-Glc synthesized in the cytosol by sucrose synthase (ADP-Glc:D-fructose 2-alpha-D-glucosyltransferase, EC 2.4.1.13)

Sequence and expression of genes encoding the large and small subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase from Chromatium vinosum

A DNA fragment bearing genes for the large (rbcL) and small (rbcS) subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) was cloned from the photosynthetic purple sulfur bacterium Chromatium vinosum. Enzymatically fully active RuBisCO was synthesized in Escherichia coli cells when the cloned DNA was placed downstream of tac promoter. Nucleotide (nt) sequences of rbcL-rbcS were more homologous to cyanobacterial counterparts than to those from Alcaligenes eutrophus or higher plants. However, the amino acid (aa) sequence in a domain responsible for CO2 activation in the C. vinosum rbcL product resembled the corresponding aa sequence in higher plant RuBisCos, but not in the cyanobacterial enzymes. Chemically determined aa sequences at the N terminals of both subunits of RuBisCO purified from C. vinosum were not identical to those deduced from the nt sequences, although they were completely the same as aa sequences deduced from rbcA-rbcB, another locus encoding RuBisCO in C. vinosum. Therefore, the rbcL-rbcS locus seems to be barely expressed under a standard condition for photoautotrophic growth. The homology of the nt sequences between rbcL and rbcA was 82%, and that between rbcS and rbcB was 63%, whereas the codon usages of these genes were basically identical. The rbcL-rbcS and rbcA-rbcB loci therefore must have evolved from a common ancestral set of genes after duplication, instead of lateral gene transfer.

Distinct properties of Escherichia coli products of plant-type ribulose-1,5-bisphosphate carboxylase/oxygenase directed by two sets of genes from the photosynthetic bacterium Chromatium vinosum

We have recently described the existence of two sets of genes encoding ribulose-1,5-bisphosphate carboxylase/oxygenase (Rbu-P2 carboxylase), rbcA-rbcB and rbcL-rbcS, in the photosynthetic purple sulfur bacterium Chromatium vinosum (Viale, A.M., Kobayashi, H., and Akazawa, T. (1989) J. Bacteriol. 171, 2391-2400). These genes were cloned in plasmid vectors, and their expression was studied in Escherichia coli. Expression of rbcA-rbcB in E. coli was obtained under the control of its own promoter. On the other hand, expression of rbcL-rbcS in this host was not observed unless these genes were cloned under the control of the tac promoter. Purified rbcA-rbcB and rbcL-rbcS products from E. coli consisted of large and small subunits in equimolar ratios. They also showed very close elution profiles to Rbu-P2 carboxylase isolated from C. vinosum in size-exclusion chromatography columns, thus suggesting hexadecameric (L8S8) structures. Vmax of Rbu-P2 carboxylase were very similar for both enzymes, but the Km values for CO2 and ribulose 1,5-bisphosphate showed some differences. Immunochemical and N-terminal amino acid sequence analyses of the large and small subunits encoded by rbcA-rbcB and rbcL-rbcS also differed, especially at the level of the small subunits. The comparisons described above as well as the analysis of C. vinosum crude extracts by anion-exchange chromatography indicated that Rbu-P2 carboxylase encoded by rbcA-rbcB was the only species detected in the photosynthetic bacterium.

Expressed genes for plant-type ribulose 1,5-bisphosphate carboxylase/oxygenase in the photosynthetic bacterium Chromatium vinosum, which possesses two complete sets of the genes

Two sets of genes for the large and small subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) were detected in the photosynthetic purple sulfur bacterium Chromatium vinosum by hybridization analysis with RuBisCO gene probes, cloned by using the lambda Fix vector, and designated rbcL-rbcS and rbcA-rbcB. rbcL and rbcA encode the large subunits, and rbcS and rbcB encode the small subunits. rbcL-rbcS was the same as that reported previously (A. M. Viale, H. Kobayashi, T. Takabe, and T. Akazawa, FEBS Lett. 192:283-288, 1985). A DNA fragment bearing rbcA-rbcB was subcloned in plasmid vectors and sequenced. We found that rbcB was located 177 base pairs downstream of the rbcA coding region, and both genes were preceded by plausible procaryotic ribosome-binding sites. rbcA and rbcD encoded polypeptides of 472 and 118 amino acids, respectively. Edman degradation analysis of the subunits of RuBisCO isolated from C. vinosum showed that rbcA-rbcB encoded the enzyme present in this bacterium. The large- and small-subunit polypeptides were posttranslationally processed to remove 2 and 1 amino acid residues from their N-termini, respectively. Among hetero-oligomeric RuBisCOs, the C. vinosum large subunit exhibited higher homology to that from cyanobacteria, eucaryotic algae, and higher plants (71.6 to 74.2%) than to that from the chemolithotrophic bacterium Alcaligenes eutrophus (56.6%). A similar situation has been observed for the C. vinosum small subunit, although the homology among small subunits from different organisms was lower than that among the large subunits.

Expression of genes for subunits of plant-type RuBisCO from Chromatium and production of the enzymically active molecule in Escherichia coli

A DNA fragment containing genes for both large (A) and small (B) subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) from a photosynthetic bacterium Chromatium vinosum was ligated with vectors for expressing unfused proteins and introduced into cells of Escherichia coli. The expressers of RuBisCO were screened on agar plates using the specific antibody raised against the native enzyme from Chromatium. The production of both subunits A and B in the expressers was demonstrated by an immunoblotting experiment. The amount of RuBisCO produced in the E. coli cells was as high as 15% of the total soluble protein after induction with isopropyl-beta-D-thiogalactoside. The specific activity of enzyme molecules produced in E. coli was nearly the same as that of the original Chromatium enzyme. On gel filtration high-performance liquid chromatography the two enzymes showed identical elution behavior, strongly indicating their similar quaternary structures.

Identification of an essential arginine residue in the beta subunit of the chloroplast ATPase

The ATPase activity of soluble chloroplast coupling factor (CF1) was irreversibly inactivated by phenylglyoxal, an arginine reagent. Under the conditions of inactivation, 2.48 mol of [14C]phenylglyoxal were incorporated per 400,000 g of enzyme when the ATPase was inactivated 50% by the reagent. Isolation of the component polypeptide subunits of the [14C]phenylglyoxal-modified enzyme revealed that the distribution of moles of labeled reagent/mol of subunit was the following: alpha, 0.37; beta, 0.40; gamma, 0.08; delta, none; epsilon, 0.03. CNBr treatment of the isolated alpha and beta subunits and fractionation of the peptides by gel electrophoresis revealed that the radioactivity bound to the alpha subunit was nonspecifically associated with several peptides, while a single peptide derived from the beta subunit contained the majority of the radioactivity associated with this subunit. After treating the isolated beta subunit with trypsin and Staphylococcus aureus protease, a major radioactive peptide was isolated with a sequence Arg-Ile-Thr-Ser-Ile-Lys. This sequence, when compared with the primary structure of the CF1 beta subunit as translated from the gene (Zurawski, G., Bottomley, W., and Whitfeld, P. R. (1982) Proc. Natl. Acad. Sci. U. S. A. 79, 6260-6264) indicated that the arginine marked with the asterisk, the predominant residue modified by phenylglyoxal when the ATPase activity of CF1 is inactivated by the reagent, is Arg 312.

Preparative purification of the subunits of chloroplast and Rhodospirillum rubrum coupling factors by flat-bed electrofocusing in granulated gels

A rapid method for the preparative purification of the subunits of oligomeric proteins like chloroplast and Rhodospirillum rubrum coupling factors is presented. It involves the dissociation of the protein in urea and the separation of its subunits by isoelectric focusing in flat-beds of Sepharose CL-4B or Sephadex G-75 superfine, in the presence of urea and in an overnight run. Using this procedure in the pH range 5-7, we have purified to homogeneity the alpha, beta and delta subunits of chloroplast coupling factor, as well as the alpha and beta subunits of Rhodospirillum rubrum coupling factor. The full separation of the gamma and epsilon subunits of chloroplast coupling factor, which focused at the same pH, was achieved by gel filtration high-performance liquid chromatography.