Expression of mature bovine H-protein of the glycine cleavage system in Escherichia coli and in vitro lipoylation of the apoform.

H-protein, a component of the glycine cleavage system with lipoic acid as a prosthetic group, was expressed in Escherichia coli using a T7 RNA polymerase plasmid expression system. After induction with 25 microM isopropyl-beta-D-thiogalactopyranoside, bacteria harboring the recombinant plasmid expressed mature bovine H-protein as a soluble form at a level of about 10% of the total bacterial protein. Little of the H-protein was lipoylated in E. coli cultured without added lipoate, but when the cells were cultured in medium supplemented with 30 microM lipoate, about 10% of the recombinant protein expressed was the correctly lipoylated active form, 10% was an inactive aberrantly modified form, presumably with an octanoyl group, and the remaining 80% was the unlipoylated apoform. Each of the three forms was purified to homogeneity and shown to have the same NH2-terminal amino acid sequence as that of native bovine H-protein. The specific activity of the lipoylated form of H-protein expressed was consistent with that of H-protein purified from bovine liver. The purified recombinant apo-H-protein was lipoylated and consequently activated in vitro with lipoyl-AMP as a lipoyl donor by lipoyltransferase purified 150-fold from bovine liver mitochondria. The lipoylation was dependent on lipoyl-AMP, apo-H-protein, and lipoyltransferase. The partially purified lipoyltransferase had no lipoate-activating activity. These results provide the first evidence that in mammals two consecutive reactions are required for the attachment of lipoic acid to the acceptor protein: the activation of lipoic acid to lipoyl-AMP catalyzed by lipoate-activating enzyme and the transfer of the lipoyl group to an N epsilon-amino group of a lysine residue to apoprotein by lipoyl-AMP:N epsilon-lysine lipoyltransferase.     

Expression and assembly of mature apotransacylase (E2b) of bovine branched-chain alpha-keto acid dehydrogenase complex in Escherichia coli. Demonstration of transacylase activity and modification by lipoylation

A cDNA clone encoding the entire transacylase (E2b) precursor of the bovine branched-chain alpha-keto acid dehydrogenase complex (Griffin, T. A., Lau, K. S., and Chuang, D. T. (1988) J. Biol. Chem. 263, 14008-14014) was used to construct a prokaryotic expression vector for recombinant mature E2b. The overexpression in Escherichia coli correlates with the presence near the 5'-terminus of the mature E2b coding region (nucleotides 20 to 28) of the sequence 5'-TCAAACT-CT-3'. It has been proposed that this sequence is involved in secondary mRNA recognition through interaction with the 5'-terminus of the bacterial 16 S rRNA. The mature E2b protein has transacylase activity when assayed with exogenous dihydrolipoamide and [1-14C] isovaleryl-CoA as substrates. However, the recombinant protein has no attached lipoic acid. This was established by the absence of radiolabel incorporation when transformed E. coli cells were grown in a medium containing DL-[2-3H]lipoic acid. The recombinant mature E2b protein was purified to greater than 95% purity in one step using Sepharose 4B column chromatography. The purified recombinant protein was shown to have a cubic 24-mer structure by electron microscopy and to possess a specific activity similar to that of the purified natural bovine E2b. The purified recombinant mature E2b was lipoylated in vitro in the presence of 2 mM ATP using a mitochondrial extract prepared from bovine liver. The above results provide the first evidence that the proper folding and assembly of mature bovine E2b is independent of the attachment of lipoyl moieties and that mammalian lipoylation activity is present in mitochondria.     

ATP synthase from bovine mitochondria: complementary DNA sequence of the import precursor of a heart isoform of the alpha subunit

The alpha-subunit of ATP synthase from mitochondria is a major component of the extrinsic membrane sector of the enzyme. It is encoded in nuclear DNA. A family of overlapping complementary DNA clones encoding its precursor has been isolated from a bovine library by using in the first instance a mixture of 128 synthetic oligonucleotides designed on the basis of the known protein sequence, and the sequence of the full-length cDNA has been determined. The deduced protein sequence shows that the alpha-subunit of ATP synthase has a presequence of 43 amino acids that is not present in the mature protein. Presumably it directs the protein into the mitochondrial matrix and is removed during the import process. The encoded protein sequence is also longer by one amino acid at its C-terminal end than the protein isolated from F1-ATPase, but this alanine residue may have been removed artifactually during release of the F1-ATPase particle from the inner mitochondrial membrane. With the exception of one uncertainty caused by an ambiguity at one position in the nucleotide sequence, the mature protein sequence encoded in the cDNA is exactly the same as the sequence determined previously by direct analysis of the protein isolated from bovine heart mitochondria [Walker et al. (1985) J. Mol. Biol. 184, 677-701]. The cDNA sequence differs in 158 nucleotides over a region of alignment of 1097 nucleotides from a partial cDNA for the alpha-subunit that has been isolated from a bovine cDNA derived from liver RNA [Breen (1988) Biochem. Biophys. Res. Commun. 152, 264-269].(ABSTRACT TRUNCATED AT 250 WORDS)     

The amino acid sequence of the 24-kDa subunit, an iron-sulfur protein, of rat liver mitochondrial NADH dehydrogenase deduced from cDNA sequence

Antiserum directed against bovine heart mitochondrial NADH dehydrogenase has been used to screen a rat liver cDNA expression library in lambda gt11. The insert cDNA of a positive clone was found to represent the 24-kDa subunit of NADH dehydrogenase by epitope selection using nitrocellulose filter containing the expressed proteins. The amino acid sequence deduced from the nucleotide sequence of the cloned cDNA indicated that the 24-kDa subunit is produced as a precursor with an amino-terminal extension, and that its mature form consists of 217 amino acid residues with a molecular weight of 23,933.     

Human complex II (succinate-ubiquinone oxidoreductase): cDNA cloning of iron sulfur (Ip) subunit of liver mitochondria

Complex II (succinate-ubiquinone oxidoreductase) is an important enzyme complex of both the tricarboxylic acid cycle and of the aerobic respiratory chains of mitochondria in eukaryotic cell and prokaryotic organisms. In this study, the amino acid sequence of iron sulfur-subunit in human liver mitochondria was deduced from cDNA which was isolated by immunoscreening a human liver lambda gtll cDNA library. An isolated clone contains an open reading frame of 786 nucleotides and encodes a mature protein of 252 amino acids with a molecular weight of 28,804. The amino acid sequence was highly homologous with that of bovine heart (94.1%) which has been determined from the purified peptide and that of Escherichia coli sdh B product (50.8%). Striking sequence conservation was found around the three cysteine-rich clusters which have been thought to comprise the iron-sulfur centers of the enzyme. This is the first report on the cDNA sequence of mitochondrial complex II.     

The primary structure of human H-protein of the glycine cleavage system deduced by cDNA cloning

A full-length cDNA encoding the human H-protein of the glycine cleavage system has been isolated from a lambda gt11 human fetal liver cDNA library. The cDNA insert was 1091 base pairs with an open reading frame of 519 base pairs which encoded a 125-amino acid mature human H-protein with a 48-amino acid presequence. Human H-protein is 97%, 86%, and 46% identical to the bovine, chicken, and pea H-protein, respectively.     

Cloning and nucleotide sequence of cDNA encoding human liver serine-pyruvate aminotransferase

Cloned cDNAs for human liver serine-pyruvate aminotransferase (Ser-PyrAT) were obtained by screening of a human liver cDNA library with a fragment of cDNA for rat mitochondrial Ser-PyrAT as a probe. Two clones were isolated from 50,000 transformants. Both clones contained approximately 1.5 kb cDNA inserts and were shown to almost completely overlap each other on restriction enzyme mapping and DNA sequencing. The nucleotide sequence of the mRNA coding for human liver Ser-PyrAT was determined from those of the cDNA clones. The mRNA comprises at least 1487 nucleotides, and encodes a polypeptide consisting of 392 amino acid residues with a molecular mass of 43,039 Da. The amino acid composition determined on acid hydrolysis of the purified enzyme showed good agreement with that deduced from the nucleotide sequence of the cDNA. In vitro translation of the mRNA derived from one of the isolated clones, pHspt12, as well as that of mRNA extracted from human liver, yielded a product of 43 kDa which reacted with rabbit anti-(rat mitochondrial Ser-PyrAT) serum. Comparison of the deduced amino acid sequences of human Ser-PyrAT and the mature form of rat mitochondrial Ser-PyrAT revealed 79.3% identity. Although human Ser-PyrAT appears to be synthesized as the mature size, the 5'-noncoding region of human Ser-PyrAT mRNA contains a nucleotide sequence which would encode, if translated, an amino acid sequence similar to that of the N-terminal extension peptide of the precursor for rat mitochondrial Ser-PyrAT.     

Chicken liver H-protein, a component of the glycine cleavage system. Amino acid sequence and identification of the N epsilon-lipoyllysine residue

The complete amino acid sequence of H-protein from chicken liver was determined by aligning peptides obtained by cyanogen bromide, endoproteinase Lys-C, Staphylococcus aureus V8 protease, and chymotrypsin cleavage together with the partial NH2- and COOH-terminal sequence of the intact protein. H-protein consists of 125 amino acids and a lipoic acid moiety linked to lysine 59. The sequence is: (sequence in text). The lysyl residue involved in lipoic acid attachment is indicated with an asterisk. The molecular weight including lipoic acid is calculated to be 13,883. From the secondary structure predicted by the method of Chou and Fasman (Chou, P. Y., and Fasman, G. D. (1978) Adv. Enzymol. 47, 45-148) the lipoic acid binding region shows alpha-helical structure and is predicted to be an interior portion of the protein from the hydropathic profile according to Kyte and Doolittle (Kyte, J., and Doolittle, R. F. (1982) J. Mol. Biol. 157, 105-132).     

Purification, characterization, and cDNA cloning of lipoate-activating enzyme from bovine liver

In mammals, lipoate-activating enzyme (LAE) catalyzes the activation of lipoate to lipoyl-nucleoside monophosphate. The lipoyl moiety is then transferred to the specific lysine residue of lipoate-dependent enzymes by the action of lipoyltransferase. We purified LAE from bovine liver mitochondria to apparent homogeneity. LAE activated lipoate with GTP at a 1000-fold higher rate than with ATP. The reaction absolutely required lipoate, GTP, and Mg(2+) ion, and the reaction product was lipoyl-GMP. LAE activated both (R)- and (S)-lipoate to the respective lipoyl-GMP, although a preference for (R)-lipoate was observed. Similarly, lipoyltransferase equally transferred both the (R)- and (S)-lipoyl moieties from the respectively activated lipoates to apoH-protein. Interestingly, however, only H-protein carrying (R)-lipoate was active in the glycine cleavage reaction. cDNA clones encoding a precursor LAE with a mitochondrial presequence were isolated. The predicted amino acid sequence of LAE is identical with that of xenobiotic-metabolizing/medium-chain fatty acid:CoA ligase-III, but an amino acid substitution due to a single nucleotide polymorphism was found. These results indicate that the medium-chain acyl-CoA synthetase in mitochondria has a novel function, the activation of lipoate with GTP.     

Molecular cloning, structural characterization and chromosomal localization of human lipoyltransferase gene.

Lipoyltransferase catalyzes the transfer of the lipoyl group from lipoyl-AMP to the lysine residue of the lipoate-dependent enzymes. We isolated human lipoyltransferase cDNA and genomic DNA. The cDNA insert contained a 1119-base pair open reading frame encoding a precursor peptide of 373 amino acids. Predicted amino acid sequence of the protein shares 88 and 31% identity with bovine lipoyltransferase and Escherichia coli lipoate-protein ligase A, respectively. Northern blot analyses of poly(A)+ RNA indicated a major species of about 1.5 kb. mRNA levels of lipoyltransferase were highest in skeletal muscle and heart, showing good correlation with those of dihydrolipoamide acyltransferase subunits of pyruvate, 2-oxoglutarate and branched-chain 2-oxo acid dehydrogenase complexes and H-protein of the glycine cleavage system which accept lipoic acid as a prosthetic group. The human lipoyltransferase gene is a single copy gene composed of four exons and three introns spanning approximately 8 kb of genomic DNA. Some alternatively spliced mRNA species were found by 5'-RACE analysis, and the most abundant species lacks the third exon. The human lipoyltransferase gene was localized to chromosome band 2q11.2 by fluorescence in situ hybridization.     

Cloning and sequence analysis of a cDNA encoding the Rieske iron-sulfur protein of rat mitochondrial cytochrome bc1 complex

We have isolated a cDNA clone for the Rieske iron-sulfur protein of rat cytochrome bc1 complex, by screening a rat liver cDNA expression library using antiserum directed against the corresponding protein of bovine. The amino acid sequence deduced from the nucleotide sequence of the cDNA indicated that the mature polypeptide of the rat protein consists of 196 amino acid residues with a molecular weight of 21,465, and that it is formed as a precursor with an amino-terminal extension. Northern blot analysis indicated that rat liver possibly contains different sizes of mRNAs for the Rieske iron-sulfur protein, and Southern blot analysis demonstrated that rats and mice possess a single gene for this protein.     

Isolation and characterization of a complementary DNA clone coding for the E1 beta subunit of the bovine branched-chain alpha-ketoacid dehydrogenase complex: complete amino acid sequence of the precursor protein and its proteolytic processing

A 1.7-kb cDNA clone encoding the entire precursor of the E1 beta subunit of the branched-chain alpha-ketoacid dehydrogenase (BCKDH) complex was isolated from a bovine liver cDNA library by screening with a mixture of synthetic oligonucleotide probes corresponding to the C-terminal five-residue sequence of the mature E1 beta subunit. A partial amino acid sequence was determined by Edman degradation of the intact subunit and the peptides generated by cleavage at the lysyl bonds. Nucleotide sequence analysis revealed that the isolated cDNA clone contained the 5'-untranslated sequence of 186 nucleotides, the translated sequence of 1176 nucleotides, and the 3'-untranslated sequence of 306 nucleotides with a poly(A) tail. A type AATAAA polyadenylation signal was located 17 nucleotides upstream of the start of a poly(A) tail. Comparison of the amino acid sequence predicted from the nucleotide sequence of the cDNA insert of the clone with the partial amino acid sequence of the mature BCKDH E1 beta subunit showed that the cDNA insert encodes for a 342 amino acid subunit with Mr 37,745 and that the subunit is synthesized as the precursor with a leader sequence of 50 amino acids and processed at the N-terminus. Northern blot analysis using the cDNA insert as a probe showed the presence of a 1.8-1.9-kb mRNA in bovine liver, suggesting that the insert covers nearly a full length of mRNA. Alignment of the deduced amino acid sequence of bovine BCKDH E1 beta with that of the human pyruvate dehydrogenase (PDH) complex E1 beta subunit revealed a high degree of sequence homology throughout the two enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nucleotide sequence of the cDNA encoding the precursor for mitochondrial serine:pyruvate aminotransferase of rat liver

The nucleotide sequence of the mRNA coding for the precursor of mitochondrial serine:pyruvate aminotransferase of rat liver was determined from those of cDNA clones. The mRNA comprises at least 1533 nucleotides, except the poly(A) tail, and encodes a polypeptide consisting of 414 amino acid residues with a molecular mass of 45,834 Da. Comparison of the N-terminal amino acid sequence of mitochondrial serine:pyruvate aminotransferase with the nucleotide sequence of the mRNA showed that the mature form of the mitochondrial enzyme consisted of 390 amino acid residues of 43,210 Da. The amino acid composition of mitochondrial serine:pyruvate aminotransferase deduced from the nucleotide sequence of the cDNA showed good agreement with the composition determined on acid hydrolysis of the purified protein. The extra 24 amino acid residues correspond to the N-terminal extension peptide (pre-sequence) that is indispensable for the specific import of the precursor protein into mitochondria. In the extension peptide there are four basic amino acids distributed among hydrophobic amino acids and, as revealed on helical wheel analysis, the putative alpha-helical structure of the peptide was amphiphilic in nature. The secondary structures of the mature serine:pyruvate aminotransferase and three other aminotransferases of rat liver were predicted from their amino acid sequences. Their secondary structures exhibited a common feature and so we propose the specific lysine residue which binds pyridoxal phosphate as the active site of serine:pyruvate aminotransferase.     

An Escherichia coli protein with homology to the H-protein of the glycine cleavage enzyme complex from pea and chicken liver.

The nucleotide sequence of an Escherichia coli gene which presumably encodes the H-protein of the glycine cleavage (GCV) enzyme complex is presented. The gene, designated gcvH, encodes a polypeptide of 128 amino acids with a calculated molecular weight of 13,665 daltons. The translation start site was determined by N-terminal amino acid sequence analysis of a gcvH-lacZ encoded fusion protein. The E. coli H-protein shows extensive homology with the H-proteins from the pea (Pisum sativum) and the chicken liver GCV enzyme complexes. 85 of 128 amino acid residues are identical or chemically similar between the E. coli and the pea H-proteins, and 74 of 128 amino acid residues are identical or chemically similar between the E. coli and the chicken liver H-proteins. All three proteins have identical amino acid sequences from residues 61-65. This sequence contains the lysyl residue involved in lipoic acid attachment in the chicken liver H-protein.     

Isolation and properties of a liver mitochondrial precursor protein to aspartate aminotransferase expressed in Escherichia coli

The precursor to rat liver mitochondrial aspartate aminotransferase has been expressed in Escherichia coli JM105 using the pKK233-2 expression vector. This mammalian natural precursor has been isolated as a soluble dimeric protein. The amino-terminal sequence and the amino acid composition of the isolated protein correspond to those predicted from the inserted cDNA (Mattingly, J. R., Jr., Rodriguez-Berrocal, F. J., Gordon, J., Iriarte, A., and Martinez-Carrion, M. (1987) Biochem. Biophys. Res. Commun. 149, 859-865). The isolated precursor contains bound pyridoxal phosphate and shows catalytic activity with a specific activity equal to that of the mature form of the enzyme. This precursor can also be processed by mitochondria into a form with the sodium dodecyl sulfate-polyacrylamide gel electrophoresis mobility of mature enzyme. The isolation of this precursor as a stable and catalytically active entity indicates that the presequence peptide does not necessarily interfere with much of the folding and basic structural properties of the mature protein component.     

The primary structure of human Rieske iron-sulfur protein of mitochondrial cytochrome bc1 complex deduced from cDNA analysis

We isolated a cDNA encoding human Rieske Fe-S protein of mitochondrial cytochrome bc1 complex from a fibroblast cDNA library by colony hybridization. The cDNA contains the nucleotide sequence encoding all of the amino acids (274 residues) comprising the putative precursor to the protein. Based on the known amino acid sequence of bovine Rieske Fe-S protein, the N-terminal extension sequence is presumed to be composed of 78 amino acids with a molecular weight of 8053. The mature protein consists of the same number of amino acid residues as that of its rat and bovine counterparts, having a homology of about 92% with the latter.     

Cloning, sequence, and expression of bovine interferon-gamma

Bovine interferon-gamma (IFN-gamma) sequences have been isolated by screening a cDNA library with a human IFN-gamma cDNA probe. The cDNA library was constructed from RNA isolated from concanavalin A-stimulated bovine lymph node cells. The open reading frame predicts that the bovine IFN-gamma precursor is composed of 166 amino acids with a predicted m.w. of 19,393. Alignment of the amino acid sequence with human IFN-gamma indicates that mature bovine IFN-gamma is composed of 143 amino acids with a predicted m.w. of 16,858. It has an amino acid homology of 63% with human IFN-gamma, and 47% with murine IFN-gamma. Biologically active bovine IFN-gamma was synthesized in an Escherichia coli expression system.     

Isolation and characterization of a complementary DNA for the nuclear-coded precursor of the beta-subunit of bovine mitochondrial F1-ATPase

We have isolated a cDNA clone encoding the precursor of the beta-subunit of the bovine heart mitochondrial F1-ATPase. Two probes were used to isolate this precursor from a bovine heart cDNA library. One probe was a mixed-sequence oligonucleotide directed against a portion of the amino acid sequence of the mature protein, and the other probe was the F1-ATPase beta-subunit gene from Saccharomyces cerevisiae. Determination of the nucleotide sequence of this cDNA reveals that it contains a 1584-nucleotide-long open reading frame that encodes the complete mature beta-subunit protein and a 48 amino acid long NH2-terminal extension. This amino-terminal presequence contains four basic arginine residues, one acidic glutamic acid residue, four polar uncharged serine residues, and five proline residues. Southern blot hybridization analyses suggest that the bovine F1-ATPase beta-subunit precursor is encoded by a single genetic locus. RNA blot hybridization analyses reveal a single mRNA species of approximately 1.9 kilobases from both bovine liver and heart.