Response of hya expression to external pH in Escherichia coli

The hya operon of Escherichia coli is composed of the genes which synthesize uptake hydrogenase isoenzyme 1 (Hyd1). Although hya expression and Hyd1 synthesis occur only under anaerobic conditions, Hyd1 is not essential for growth. In this study we used a hya'-'lacZ fusion to characterize parameters of anaerobic growth that maximize hya expression in an attempt to further elucidate Hyd1 function. We found that the expression pattern of hya followed a decline of external pH. In buffered media where the pH value was set, the onset of hya expression initiated earlier in growth and reached a greater peak level in acidic than in alkaline medium. When cultures expressing hya were shifted from acidic to alkaline conditions, hya expression was arrested; shifting from alkaline to acidic conditions stimulated hya expression. Maximal expression of hya under all growth conditions required the sigma factor RpoS and transcriptional regulators AppY and ArcA. In the absence of RpoS or AppY, the response of hya expression onset to external pH was evident and maximal hya levels remained greater in acidic than in alkaline medium. However, the absence of ArcA led to a diminished response of expression onset to external pH and the loss of elevated expression at an acidic external pH. The fermentation end product formate slightly altered hya expression levels but was not required for hya to respond to external pH. In contrast to hya expression, the onset of hyb operon expression, encoding uptake hydrogenase isoenzyme 2, was constitutive with respect to external pH. However, external pH did affect hyb expression levels, which, in contrast to hya, were maximal in alkaline rather than acidic medium.

Electron paramagnetic resonance (EPR) studies on hydrogenase-1 (HYD1) purified from a mutant strain (AP6) of Escherichia coli enhanced in HYD1

Hydrogenase-1 (HYD1), overexpressed by twofold, has been purified to homogeneity and to a high specific activity from a mutant strain (AP6) of Escherichia coli which lacks hydrogenase-2. Plasma emission spectroscopy indicated that 0.93 atom of nickel and 11.4 iron atoms were present in HYD1. EPR studies on the as isolated HYD1 detected a complex 3Fe-4S signal and a Ni(III) species. Reduction with hydrogen gas caused disappearance of both the 3Fe-4S cluster and initial Ni(III) signals. At the same time the EPR signature (small g = 2.19 signal) of the activated hydrogenase appeared. The detection of a 4Fe-4S cluster signal was noted. Reduction of HYD1 with sodium dithionite caused all nickel signals to disappear. The 4Fe-4S complex intensity was slightly increased. The EPR responses in the three oxidation-reduction states are consistent with other known (NiFe)-hydrogenases.

Cloning, sequencing and overexpression of the Desulfovibrio gigas ferredoxin gene in E. coli

We have cloned the gene encoding Desulfovibrio gigas ferredoxin using a photodigoxigenin-labelled probe synthesized with the polymerase chain reaction. The DNA sequence of the gene predicts a polypeptide of 58 residues after removal of the initial formyl methionine (polypeptide M(r) = 6,276). The ferredoxin gene was expressed in aerobically grown E. coli behind the lac promoter of pUC18 resulting in a high level of ferredoxin expression which comprises about 10% of the total cell protein. EPR analysis of recombinant ferredoxin revealed the presence of a [3Fe-4S] cluster which is characteristic of native D. gigas ferredoxin II.

Cloning, sequencing, and mutational analysis of the hyb operon encoding Escherichia coli hydrogenase 2

The genes encoding the two structural subunits of Escherichia coli hydrogenase 2 (HYD2) have been cloned and sequenced. They occur in an operon (hyb) which contains seven open reading frames. An hyb deletion mutant (strain AP3) failed to grown on dihydrogen-fumarate medium and also produced very low levels of HYD1. All seven open reading frames are required for restoration of wild-type levels of active HYD2 in AP3. The hyb operon was mapped at 65 min on the E. coli chromosome.

Carboxy-terminal processing of the large subunit of [NiFe] hydrogenases

Two electrophoretic forms of the large subunit of the soluble periplasmic [NiFe] hydrogenase from Desulfovibrio gigas have been detected by Western analysis. The faster moving form co-migrates with the large subunit from purified, active enzyme. Amino acid sequence and composition of the C-terminal tryptic peptide of the large subunit from purified hydrogenase revealed that it is 15 amino acids shorter than that predicted by the nucleotide sequence. Processing of the nascent large subunit occurs by C-terminal cleavage between His536 and Val537, residues which are highly conserved among [NiFe] hydrogenases. Mutagenesis of the analogous residues, His582 and Val583, in the E. coli hydrogenase-1 (HYD1) large subunit resulted in significant decrease in processing and HYD1 activity.

Structure-function relationships among the nickel-containing hydrogenases

The enzymology of the heterodimeric (NiFe) and (NiFeSe) hydrogenases, the monomeric nickel-containing hydrogenases plus the multimeric F420-(NiFe) and NAD(+)-(NiFe) hydrogenases are summarized and discussed in terms of subunit localization of the redox-active nickel and non-heme iron clusters. It is proposed that nickel is ligated solely by amino acid residues of the large subunit and that the non-heme iron clusters are ligated by other cysteine-rich polypeptides encoded in the hydrogenase operons which are not necessarily homologous in either structure or function. Comparison of the hydrogenase operons or putative operons and their hydrogenase genes indicate that the arrangement, number and types of genes in these operons are not conserved among the various types of hydrogenases except for the gene encoding the large subunit. Thus, the presence of the gene for the large subunit is the sole feature common to all known nickel-containing hydrogenases and unites these hydrogenases into a large but diverse gene family. Although the different genes for the large subunits may possess only nominal general derived amino acid homology, all large subunit genes sequenced to date have the sequence R-X-C-X-X-C fully conserved in the amino terminal region of the polypeptide chain and the sequence of D-P-C-X-X-C fully conserved in the carboxyl terminal region. It is proposed that these conserved motifs of amino acids provide the ligands required for the binding of the redox-active nickel. The existing EXAFS (Extended X-ray Absorption Fine Structure) information is summarized and discussed in terms of the numbers and types of ligands to the nickel and the various redox species of nickel defined by EPR spectroscopy. New information concerning the ligands to nickel is presented based on site-directed mutagenesis of the gene encoding the large subunit of the (NiFe) hydrogenase-1 of Escherichia coli. Based on considerations of the biochemical, molecular and biophysical information, ligand environments of the nickel in different redox states of the (NiFe) hydrogenase are proposed.

Mutational analysis and characterization of the Escherichia coli hya operon, which encodes [NiFe] hydrogenase 1

Deletion mutants of Escherichia coli specific for hydrogenase isoenzyme 1 (HYD1) have been constructed and characterized. The hya operon, which contains genes for the two HYD1 structural subunits and four additional genes, was mapped at 22 min on the E. coli chromosome. The total hydrogenase activities of the HYD1-negative mutant and wild-type strains were similar. However, the formate dehydrogenase activity associated with the formate hydrogen lyase pathway was lower in the mutant. The hya mutant (strain AP1), complemented with only the hydrogenase structural genes (hyaAB), produced antigenically identifiable but inactive HYD1 protein. The first five genes of hya (hyaA to hyaE) were required for the synthesis of active HYD1, but wild-type levels of HYD1 activity were restored only when mutant cells were transformed with all six genes of the operon. When AP1 was complemented with hya carried on a high-copy-number plasmid, the HYD1 structural subunits were overexpressed, but the excess protein was unprocessed and localized in the soluble fraction of the cell. The products of hyaDEF are postulated to be involved in the processing of nascent structural subunits (HYAA and HYAB). This processing takes place only after the subunits are inserted into the cell membrane. It is concluded that the biosynthesis of active HYD1 is a complex biochemical process involving the cellular localization and processing of nascent structural subunits, which are in turn dependent on the insertion of nickel into the nascent HYD1 large subunit.

Localization of membrane-associated (NiFe) and (NiFeSe) hydrogenases of Desulfovibrio vulgaris using immunoelectron microscopic procedures

The intracellular location of membrane-associated (NiFe) and (NiFeSe) hydrogenases of Desulfovibrio vulgaris was determined using pre-embedding and post-embedding immunoelectron microscopic procedures. Polyclonal antisera directed against the purified (NiFe) and (NiFeSe) hydrogenases were raised in rabbits. One-day-old cultures of D. vulgaris, grown on a lactate/sulfate medium, were used for all experiments in these studies. For post-embedding labeling studies cells were fixed with 0.2% glutaraldehyde and 0.3% formaldehyde, dehydrated with methanol, and embedded in the low-temperature resin Lowicryl K4M. Our post-embedding studies using antibody-gold or protein-A-gold as electron-dense markers revealed the location of the two hydrogenases exclusively at the cell periphery; the precise membrane location was then demonstrated by pre-embedding labeling. Spheroplasts were incubated with the polyclonal antisera against (NiFe) and (NiFeSe) hydrogenase followed by ferritin-linked secondary antibodies prior to embedding and sectioning. The observed labeling pattern unequivocally revealed that the antigenic reactive sites of the (NiFe) hydrogenase are located in the near vicinity of the cytoplasmic membrane facing into the periplasmic space, whereas the (NiFeSe) hydrogenase is associated with the cytoplasmic side of the cytoplasmic membrane.

Cloning and sequencing of a putative Escherichia coli [NiFe] hydrogenase-1 operon containing six open reading frames

DNA encompassing the structural genes of an Escherichia coli [NiFe] hydrogenase has been cloned and sequenced. The genes were identified as those encoding the large and small subunits of hydrogenase isozyme 1 based on NH2-terminal sequences of purified subunits (kindly provided by K. Francis and K. T. Shanmugam). The structural genes formed part of a putative operon that contained four additional open reading frames. We have designated the operon hya and the six open reading frames hyaA through F. hyaA and hyaB encode the small and large structural subunits, respectively. The nucleotide-derived amino acid sequence of hyaC has a calculated molecular mass of 27.6 kilodaltons, contains 20% aromatic residues, and has four potential membrane-spanning regions. Open reading frames hyaD through F could encode polypeptides of 21.5, 14.9, and 31.5 kilodaltons, respectively. These putative peptides have no homology to other reported protein sequences, and their functions are unknown.

Analysis and comparison of nucleotide sequences encoding the genes for [NiFe] and [NiFeSe] hydrogenases from Desulfovibrio gigas and Desulfovibrio baculatus

The nucleotide sequences encoding the [NiFe] hydrogenase from Desulfovibrio gigas and the [NiFeSe] hydrogenase from Desulfovibrio baculatus (N.K. Menon, H.D. Peck, Jr., J. LeGall, and A.E. Przybyla, J. Bacteriol. 169:5401-5407, 1987; C. Li, H.D. Peck, Jr., J. LeGall, and A.E. Przybyla, DNA 6:539-551, 1987) were analyzed by the codon usage method of Staden and McLachlan. The reported reading frames were found to contain regions of low codon probability which are matched by more probable sequences in other frames. Renewed nucleotide sequencing showed the probable frames to be correct. The corrected sequences of the two small and large subunits share a significant degree of sequence homology. The small subunit, which contains 10 conserved cysteine residues, is likely to coordinate at least 2 iron-sulfur clusters, while the finding of a selenocysteine codon (TGA) near the 3' end of the [NiFeSe] large-subunit gene matched by a regular cysteine codon (TGC) in the [NiFe] large-subunit gene indicates the presence of some of the ligands to the active-site nickel in the large subunit.

The three classes of hydrogenases from sulfate-reducing bacteria of the genus Desulfovibrio

Three types of hydrogenases have been isolated from the sulfate-reducing bacteria of the genus Desulfovibrio. They differ in their subunit and metal compositions, physico-chemical characteristics, amino acid sequences, immunological reactivities, gene structures and their catalytic properties. Broadly, the hydrogenases can be considered as 'iron only' hydrogenases and nickel-containing hydrogenases. The iron-sulfur-containing hydrogenase ([Fe] hydrogenase) contains two ferredoxin-type (4Fe-4S) clusters and an atypical iron-sulfur center believed to be involved in the activation of H2. The [Fe] hydrogenase has the highest specific activity in the evolution and consumption of hydrogen and in the proton-deuterium exchange reaction and this enzyme is the most sensitive to CO and NO2-. It is not present in all species of Desulfovibrio. The nickel-(iron-sulfur)-containing hydrogenases [( NiFe] hydrogenases) possess two (4Fe-4S) centers and one (3Fe-xS) cluster in addition to nickel and have been found in all species of Desulfovibrio so far investigated. The redox active nickel is ligated by at least two cysteinyl thiolate residues and the [NiFe] hydrogenases are particularly resistant to inhibitors such as CO and NO2-. The genes encoding the large and small subunits of a periplasmic and a membrane-bound species of the [NiFe] hydrogenase have been cloned in Escherichia (E.) coli and sequenced. Their derived amino acid sequences exhibit a high degree of homology (70%); however, they show no obvious metal-binding sites or homology with the derived amino acid sequence of the [Fe] hydrogenase. The third class is represented by the nickel-(iron-sulfur)-selenium-containing hydrogenases [( NiFe-Se] hydrogenases) which contain nickel and selenium in equimolecular amounts plus (4Fe-4S) centers and are only found in some species of Desulfovibrio. The genes encoding the large and small subunits of the periplasmic hydrogenase from Desulfovibrio (D.) baculatus (DSM 1743) have been cloned in E. coli and sequenced. The derived amino acid sequence exhibits homology (40%) with the sequence of the [NiFe] hydrogenase and the carboxy-terminus of the gene for the large subunit contains a codon (TGA) for selenocysteine in a position homologous to a codon (TGC) for cysteine in the large subunit of the [NiFe] hydrogenase. EXAFS and EPR studies with the 77Se-enriched D. baculatus hydrogenase indicate that selenium is a ligand to nickel and suggest that the redox active nickel is ligated by at least two cysteinyl thiolate and one selenocysteine selenolate residues.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of three classes of hydrogenase in the genus, Desulfovibrio

A comparison of amino-terminal amino acid sequences from the large and small subunits of hydrogenases from Desulfovibrio reveals significant differences. These results, in conjunction with antibody analyses, clearly indicate that the iron, iron + nickel, and iron + nickel + selenium containing hydrogenases represent three distinct classes of hydrogenase in Desulfovibrio.

Cloning, characterization, and sequencing of the genes encoding the large and small subunits of the periplasmic [NiFe]hydrogenase of Desulfovibrio gigas

The structural genes for the large and small subunits of Desulfovibrio gigas periplasmic [NiFe]hydrogenase were identified and isolated by immunological and oligonucleotide screening. The gene for the small subunit codes for a 266-amino-acid, 28,724-dalton polypeptide which is separated by 63 nucleotides from the large subunit gene that codes for a 560-amino-acid, 61,707-dalton polypeptide. A putative signal peptide precedes the small subunit coding region, which may direct transport of the enzyme into the periplasmic compartment. Comparison of the amino acid sequence of this enzyme with those of two other classes of hydrogenase found in Desulfovibrio revealed that the D. gigas periplasmic hydrogenase has some homologies to the periplasmic [NiFeSe]hydrogenase of D. baculatus but none to the periplasmic [Fe]hydrogenase of D. vulgaris. The genes for the large and small subunits of the D. gigas hydrogenase hybridize strongly to genomic DNAs from several species of Desulfovibrio, indicating molecular similarity of the [NiFe]hydrogenase among sulfate reducers.

Cloning and sequencing of the genes encoding the large and small subunits of the periplasmic (NiFeSe) hydrogenase of Desulfovibrio baculatus

The genes coding for the large and small subunits of the periplasmic hydrogenase from Desulfovibrio baculatus have been cloned and sequenced. The genes are arranged in an operon with the small subunit gene preceding the large subunit gene. The small subunit gene codes for a 32 amino acid leader sequence supporting the periplasmic localization of the protein, however no ferredoxin-like or other characteristic iron-sulfur coordination sites were observed. The periplasmic hydrogenases from D. baculatus (an NiFeSe protein) and D. vulgaris (an Fe protein) exhibit no homology suggesting that they are structurally different, unrelated entities.

Cloning of the 3'-phosphoadenylyl sulfate reductase and sulfite reductase genes from Escherichia coli K-12

The structural genes for 3'-phosphoadenylyl sulfate (PAPS) reductase (cysH) and sulfite reductase (alpha and beta subunits; EC 1.8.1.2)(cysI and cysJ) of Escherichia coli K-12 have been cloned by complementation. pCYSI contains two PstI fragments (18.3 and 2.9 kb) which complement cysH-, cysI-, and cysJ- mutants. Subcloning showed that the cysH gene is located on a 1.6-kb ClaI subfragment (pCYSI-3) whereas cysI and most of cysJ are carried on a 3.7-kb ClaI subfragment (pCYSI-5). The PAPS reductase gene is closely linked to the sulfite reductase genes, but its expression is regulated by a unique promoter. The cysI and cysJ genes, on the other hand, are transcribed as an operon and the promoter precedes the cysI gene. Maxicell analysis demonstrated that pCYSI encodes three polypeptides of Mr 27,000, 57,000, and 60,000, in addition to the tetracycline-resistance determinant. The 60- and 57-kDa proteins are most likely the alpha and beta subunits, respectively, of E. coli sulfite reductase while the 27-kDa protein is putatively identified as PAPS reductase. Preliminary data suggest that the alpha and beta subunits of sulfite reductase are encoded by cysI and cysJ, respectively.

Putative signal peptide on the small subunit of the periplasmic hydrogenase from Desulfovibrio vulgaris

We sequenced the NH2 terminus of the large and small subunits of the periplasmic hydrogenase from the sulfate-reducing bacterium Desulfovibrio vulgaris (Hildenborough) and found that the small subunit lacks a region of 34 NH4-terminal amino acids coded by the gene for the small subunit (G. Voordouw and S. Brenner, Eur. J. Biochem. 148:515-520, 1985). We suggest that this region constitutes a signal peptide based on comparison with known procaryotic signal peptides.

Complementation of an Escherichia coli pyrF mutant with DNA from Desulfovibrio vulgaris

A PyrF- mutant of Escherichia coli (SK1108, pyrF::Tn5 Kanr) was complemented with the Desulfovibrio vulgaris (Hildenborough) structural gene for orotidine-5'-phosphate decarboxylase (EC 4.1.1.23). Either orientation of a 1.6-kilobase-pair D. vulgaris DNA fragment (pLP3B or pLP3A) complemented the PyrF- strain suggesting that the D. vulgaris pyrF promoter was functional. The apparent product of the D. vulgaris pyrF gene was a single 26-kilodalton polypeptide. These results demonstrate the utility of E. coli cloning systems in studying metabolic and energetic pathways in sulfate-reducing bacteria.

Isolation of biologically active ribonucleic acid from sources enriched in ribonuclease

Intact ribonucleic acid (RNA) has been prepared from tissues rich in ribonuclease such as the rat pancreas by efficient homogenization in a 4 M solution of the potent protein denaturant guanidinium thiocyanate plus 0.1 M 2-mercaptoethanol to break protein disulfide bonds. The RNA was isolated free of protein by ethanol precipitation or by sedimentation through cesium chloride. Rat pancreas RNA obtained by these means has been used as a source for the purification of alpha-amylase messenger ribonucleic acid.

Isolation and in vitro translation of the messenger RNA coding for pancreatic amylase

RNA prepared from dog pancreas polysomes or microsomes directs the synthesis of pancreas-specific proteins in heterologous cell-free translation systems. A translation product, approximately 1500 daltons larger than authentic amylase, corresponding to pancreatic amylase was identified by immunoprecipitation with anti-amylase gamma-globulin and tryptic peptide analysis. We suggest that this larger form of amylase is an amylase precursor. Using amylase immunoprecipitation of reticulocyte translation reactions as an assay, we have shown that greater than 99% of the mRNA for amylase is associated with polysomes bound to the endoplasmic reticulum. Electrophoresis of pancreatic mRNA preparations in formamide-containing polyacrylamide gels and subsequent translation of the fractions have shown that amylase mRNA is of a discrete size with a mobility equivalent to that of 18 S ribosomal RNA, and therefore significantly larger than required to code solely for the amino acid sequence of the amylase precursor.