Biomedical subjects

B Dunbar

Publications and source records attributed to B Dunbar.

At least 37 records · Page 2Linked to original sources

PubMed1991

Transport of proteins into chloroplasts. Delineation of envelope "transit" and thylakoid "transfer" signals within the pre-sequences of three imported thylakoid lumen proteins.

The targeting of cytosolically synthesized proteins into the thylakoid lumen is mediated by an aminoterminal pre-sequence consisting of an "envelope transit" and a "thylakoid transfer" signal in tandem. We have investigated the structural characteristics of several thylakoid transfer signals by determining the intermediate sites at which the stromal processing peptidase cleaves to remove the transit sequences. Using this approach we have found that the thylakoid transfer signals of Silene pratensis plastocyanin, 23-kDa oxygen-evolving complex protein from wheat, and 33-kDa oxygen-evolving complex protein from wheat, are 25, 39, and 48 residues in length, respectively. All of the transfer signals contain hydrophobic core sequences and a "-3,-1" motif reminiscent of those found in signal sequences, but the amino-terminal regions of the transfer signals of the 23- and 33-kDa proteins are both longer and more highly charged. The net charge of each amino-terminal region of the transfer sequences is +1, including the amino-terminal amino group. In each case, the stromal processing peptidase cleaves immediately after a positively charged residue, but otherwise the cleavage sites exhibit no common elements of either primary or secondary structure.

Amino Acid Sequence↗

PubMed1991

Direct electrochemistry of two genetically distinct flavodoxins isolated from Azotobacter chroococcum grown under nitrogen-fixing conditions.

Two genetically distinct flavodoxins, designated AcFldA and AcFldB, were isolated from Azotobacter chroococcum (MCD1155) grown under nitrogen-fixing conditions. AcFldA and AcFldB differ in their midpoint potentials for the semiquinone-hydroquinone couple (Em -305 mV and -520 mV respectively). Only AcFldB was competent to act as an electron donor to the Mo-containing nitrogenase of A. chroococcum. The N-terminal amino acid sequence (20 residues) of AcFldB was identical with that predicted from the nifF DNA sequence of A. vinelandii OP [Bennett, Jacobsen & Dean (1988) J. Biol. Chem. 263, 1364-1369], suggesting that AcFldB is the nifF gene product of A. chroococcum (MCD1155). Direct fast reversible electrochemistry of these flavodoxins has been achieved at a polished edge-plane graphite electrode using the aminoglycoside neomycin as a promoter. The heterogeneous rates of electron transfer between the graphite electrode and AcFldA and AcFldB were determined to be 1.2 x 10(-3) cm.s-1 and 2.0 x 10(-3) cm.s-1 respectively. The natures of two minor species of flavodoxin designated AcFldC and AcFldD, which were resolved by f.p.l.c., are also discussed.

Amino Acid Sequence↗

PubMed1991

Site-directed chemical conversion of serine to cysteine in penicillin acylase from Escherichia coli ATCC 11105. Effect on conformation and catalytic activity.

Penicillin acylase (EC 3.5.1.11) was completely inactivated with equimolar phenylmethane [35S]sulphonyl fluoride (PhMe35SO2F); the stability of the sulphonyl group in the modified protein was determined by measurement of the radioactivity in ultrafiltrates. In 8 M urea, the rate of loss of the sulphonyl group was similar to that observed in PhMeSO2F-inactivated chymotrypsin [Gold, A.M. & Fahrney, D. (1964) Biochemistry 3, 783-791]. Incubation of the PhMeSO2F-inactivated acylase with 0.7 M potassium thioacetate yielded an acetylthiol enzyme which was subsequently converted to a thiol-enzyme during incubation with 10 mM 6-aminopenicillanic acid. 4-Pyridyl-ethylcysteine was released by acid hydrolysis after reaction of the thiol-protein with 4-vinylpyridine. The rates of reaction of thiol-penicillin acylase with iodoacetic acid and 2,2'-dipyridyl disulphide were consistent with the presence of an incompletely accessible cysteinyl sidechain. After carboxymethylating the thiol-enzyme with iodo[2-3H]acetic acid, the label was shown by SDS/PAGE and sequencing analysis to be associated exclusively with the beta-chain NH2-terminal residue, indicating conversion of Ser290 to S-carboxymethyl-cysteine. Near-ultraviolet CD spectra showed the conformation of thiol-penicillin acylase to be indistinguishable from that of the native protein but the catalytic activity was less than 0.02% of that of the normal enzyme. The possibility that Ser290 acts as a nucleophile in catalysis is discussed.

Amino Acid Sequence↗

PubMed1990

The plant mitochondrial F1-ATPase. The identity of the delta' (20 kDa) subunit.

The N-terminal amino acid sequence of the 20 kDa (delta') subunit of the turnip (Brassica napus L.) mitochondrial F1-ATPase has been determined. Comparison of the sequence obtained with those of the epsilon subunits of chloroplast CF1, E. coli F1 and the delta subunit of bovine F1 shows that the turnip delta' subunit is another member of this family of homologous proteins. The delta' subunit of sweet potato F1-ATPase [(1989) J. Biol. Chem. 264, 3183-3186] is very similar to the turnip sequence and thus can also be considered to belong to this family.

Amino Acid Sequence↗

PubMed1990

Limited proteolysis of beta 2-microglobulin at Lys-58 by complement component C1s.

We have now demonstrated that activated complement component C1s cleaves beta 2-microglobulin at the position identical to that at which beta 2-microglobulin is cleaved in serum of patients suffering from lung cancer. The main cleavage is in the disulphide loop C-terminal to Lys-58, generating a modified form of beta 2-microglobulin with a two-chain structure. The C-terminal Lys-58 in the A chain is highly susceptible to removal by a carboxypeptidase-B-like activity causing the formation of des-Lys58-beta 2-microglobulin. This is the first demonstration of a noncomplement protein substrate for the proteolytic activity of C1s. The C1s-induced cleavage of beta 2-microglobulin can be inhibited in the presence of C1 esterase inhibitor, demonstrating a regulatory function of C1 esterase inhibitor in the C1s-induced cleavage of beta 2-microglobulin.

Amino Acid Sequence↗

PubMed1990

Identification and characterization of a GroEL homologue in Rhodobacter sphaeroides.

A protein closely related to the Escherichia coli GroEL protein has been isolated from Rhodobacter sphaeroides. Native and SDS-polyacrylamide gel electrophoresis of this protein have shown that it is present in the cell as a multimeric complex of Mr 670,000 which is composed of a monomer of Mr 58,000. Antisera raised against the Mr 58,000 polypeptide have been shown to cross-react with GroEL and the alpha subunit of the pea plastid chaperonin. The N-terminal amino acid sequence of the Mr 58,000 polypeptide is identical to that of GroEL at 15 of 19 residues and is also closely related to the alpha subunit of the pea plastid chaperonin, though less so to the beta subunit.

Amino Acid Sequence↗

PubMed1990

N-terminal amino acid sequence identity between a major allergen of Ascaris lumbricoides and Ascaris suum, and MHC-restricted IgE responses to it.

A protein allergen of the parasitic nematode Ascaris has been purified to homogeneity by immunoaffinity chromatography. It is the most abundant protein species in the parasite's body fluid and has been named ABA-1. The allergen's molecular weight (MW) has been previously estimated at 14,000, but this sizing is currently under re-evaluation. The immunological activity of the protein was intact after purification, as attested by immunoprecipitation and passive cutaneous anaphylaxis. The IgE response to ABA-1 was under major histocompatibility complex (MHC) restriction in the rat, in which only RT1u strains were found to respond following infection with the parasite. The tissue-invasive and intestinal stages of both Ascaris lumbricoides (of humans) and Ascaris suum (of pigs) have an antigen of similar MW to ABA-1 in their secretions or among their somatic antigens. These are antigenically indistinguishable; they were found to have similar amino acid compositions, and their N-terminal amino acid sequences were identical to 41 residues. Finally, the apparent MW, amino acid composition and isoelectric point of ABA-1 all argue for close similarity to the previously described Allergen A of the parasite.

Allergens↗

PubMed1989

The reaction specificities of the thylakoidal processing peptidase and Escherichia coli leader peptidase are identical.

Proteins which are transported across the bacterial plasma membrane, endoplasmic reticulum and thylakoid membrane are usually synthesized as larger precursors containing amino-terminal targeting signals. Removal of the signals is carried out by specific, membrane-bound processing peptidases. In this report we show that the reaction specificities of these three peptidases are essentially identical. Precursors of two higher plant thylakoid lumen proteins are efficiently processed by purified Escherichia coli leader peptidase. Processing of one precursor, that of the 23 kd photosystem II protein, by both the thylakoidal and E. coli enzymes generates the correct mature amino terminus. Similarly, leader (signal) peptides of both eukaryotic and prokaryotic origin are cleaved by partially purified thylakoidal processing peptidase. No evidence of incorrect processing was obtained. Both leader peptidase and thylakoidal peptidase are inhibited by a synthetic leader peptide.

Amino Acid Sequence↗

PubMed1989

Plant mitochondrial F1-ATPase. The presence of oligomycin-sensitivity-conferring protein (OSCP).

Purified pea (Pisum sativum) cotyledon F1-ATPase contains six subunits rather than the five usually reported for F1-ATPases. The additional 26.5 kDa (delta) subunit is shown by immunoblotting and N-terminal amino acid sequencing to be similar to bovine oligomycin-sensitivity-conferring protein (OSCP). It is concluded that the delta subunit of plant mitochondrial F1-ATPase is the plant OSCP. This OSCP subunit occurs in all mono- and di-cotyledonous species of plants tested (maize, oats, peas, potatoes, sweet potatoes and turnips).

Adenosine Triphosphatases↗

PubMed1989

Component X of mammalian pyruvate dehydrogenase complex: structural and functional relationship to the lipoate acetyltransferase (E2) component.

The lipoate acetyltransferase (E2, Mr 70,000) and protein X (Mr 51,000) subunits of the bovine pyruvate dehydrogenase multienzyme complex (PDC) core assembly are antigenically distinct polypeptides. However comparison of the N-terminal amino acid sequence of the E2 and X polypeptides reveals significant homology between the two components. Selective tryptic release of the 14C-labelled acetylated lipoyl domains of E2 and protein X from native PDC generates stable, radiolabelled 34 and 15 kDa fragments, respectively. Thus, in contrast to E2 which contains two tandemly-arranged lipoyl domains, protein X appears to contain only a single lipoyl domain located at its N-terminus.

Acetyltransferases↗

PubMed1989

Posthemorrhagic hydrocephalus in high-risk preterm infants: natural history, management, and long-term outcome.

The natural history, medical management, and outcome in infants with progressive posthemorrhagic hydrocephalus after intraventricular hemorrhage were studied prospectively. Infants with asymptomatic severe posthemorrhagic hydrocephalus were managed with a predetermined protocol. Outcome between groups at 1 to 2 years and at more than 3 years was compared. The natural history study, restricted to the inborn population, revealed that posthemorrhagic hydrocephalus developed in 53 of 409 infants with intraventricular hemorrhage. The progression of hydrocephalus either was arrested or regressed in 35 of 53 infants; progression to severe hydrocephalus occurred in 18 of 53 infants. The severe posthemorrhagic hydrocephalus was asymptomatic in 16 of 18 infants. The management and outcome study included both inborn and outborn infants. Of 50 infants, 12 had symptomatic severe hydrocephalus and 38 had asymptomatic severe hydrocephalus. The 16 infants managed with close observation were as likely to remain shunt free as the 22 infants managed with serial lumbar punctures. Of 38 infants, 20 were managed without shunts. At 3 to 6 years, the outcome of infants in the close observation group did not differ from that in the lumbar puncture group. Long-term outcome of infants with progression to asymptomatic severe hydrocephalus did not differ from that of infants in whom disease progression was arrested. Poor outcome in infants with intraventricular hemorrhage and subsequent posthemorrhagic hydrocephalus was related to severity of hemorrhage and gestational age at birth less than 30 weeks. Because long-term outcome of infants with severe hydrocephalus did not differ from that of infants in whom the progression of hydrocephalus was arrested or whose condition improved before hydrocephalus became severe, we currently attempt medical management of these infants.

Brain Damage, Chronic↗

PubMed1989

Insect immunity: isolation from immune blood of the dipteran Phormia terranovae of two insect antibacterial peptides with sequence homology to rabbit lung macrophage bactericidal peptides.

We have isolated from the hemolymph of immunized larvae of the dipteran insect Phormia terranovae two peptides that are selectively active against Gram-positive bacteria. They are positively charged peptides of 40 residues containing three intramolecular disulfide bridges and differ from one another by only a single amino acid. These peptides are neither functionally nor structurally related to any known insect immune response peptides but show significant homology to microbicidal cationic peptides from mammalian granulocytes (defensins). We propose the name "insect defensins" for these insect antibiotic peptides.

Amino Acid Sequence↗

PubMed1988

Complete amino acid sequence of the neurone-specific gamma isozyme of enolase (NSE) from human brain and comparison with the non-neuronal alpha form (NNE).

The complete amino acid sequence (433 residues) of the human neurone-specific gamma isozyme of enolase (NSE) has been determined by a combination of direct amino acid sequencing and nucleotide sequencing of cloned cDNA. Substantial amino acid sequence of the non-neuronal alpha form of the enzyme was also obtained which agreed almost entirely with the indirect cDNA sequence. Comparison of the two human sequences shows no insertions or deletions, but 72 replacements. Comparison of the human gamma form with the corresponding isozyme from the rat shows only 7 replacements (compared to 27 changes between the human and rat alpha isozymes). We have identified regions of sequence difference between the human alpha and gamma forms that are mainly hydrophilic in character (residues 271-285, 298-316 and 416-433). These residues are on the surface of the three-dimensional structure and could be useful as immunogens to produce antibodies specific for the neurone-specific form.

Amino Acid Sequence↗

PubMed1988

Genomic and cDNA cloning of the human C1 inhibitor. Intron-exon junctions and comparison with other serpins.

Amino acid sequencing of trypsin fragments of C1 inhibitor gave regions of low codon degeneracy that were used for oligonucleotide probes. Human liver cDNA libraries gave clones containing most of the protein sequence, showing that the inhibitory domain belongs to the 'serpin' class of protein inhibitors. Fragments of these cDNA clones were used to probe human genomic cosmid libraries. The genomic sequence was found to be about 17 X 10(3) base pairs, with a coding sequence of approximately 1800 base pairs containing introns at amino acid positions--6, 162, 207, 275, 321, 395, and one in the 5' non-coding region. There is very little similarity of intron position amongst the serpin genes. All but one of the intron positions in the C1 inhibitor structural gene correspond to surface residues if C1 inhibitor is considered to have a structure similar to the cleaved form of alpha 1-antiproteinase. The serine and threonine residues in the N-terminal 100 amino acids of the sequence thought to carry complex carbohydrates are found in a single exon.

Amino Acid Sequence↗

PubMed1988

The complete amino acid sequence of human skeletal-muscle fructose-bisphosphate aldolase.

The complete amino acid sequence of human skeletal-muscle fructose-bisphosphate aldolase, comprising 363 residues, was determined. The sequence was deduced by automated sequencing of CNBr-cleavage, o-iodosobenzoic acid-cleavage, trypsin-digest and staphylococcal-proteinase-digest fragments. Comparison of the sequence with other class I aldolase sequences shows that the mammalian muscle isoenzyme is one of the most highly conserved enzymes known, with only about 2% of the residues changing per 100 million years. Non-mammalian aldolases appear to be evolving at the same rate as other glycolytic enzymes, with about 4% of the residues changing per 100 million years. Secondary-structure predictions are analysed in an accompanying paper [Sawyer, Fothergill-Gilmore & Freemont (1988) Biochem. J. 249, 789-793].

Amino Acid Sequence↗

PubMed1988

Insect immunity. Purification and characterization of a family of novel inducible antibacterial proteins from immunized larvae of the dipteran Phormia terranovae and complete amino-acid sequence of the predominant member, diptericin A.

Injury or injection of live bacteria into third instar larvae of the dipteran insect Phormia terranovae results in the appearance in the haemolymph of at least five groups of heat-stable, more or less basic peptides with antibacterial activity against Escherichia coli. Three of these peptides have been purified. The amino acid sequence has been completely established for one of these and partially (first 40 residues from the N-terminus) for the two others. The sequences show marked homologies indicating that the three peptides belong to a common family. They are not related to other known antibacterial peptides from insects [lysozymes, cecropins (including sarcotoxin I) and attacins]. We propose the name of diptericins for this new family of antibiotic molecules.

Amino Acid Sequence↗

PubMed1987

Molecular cloning of cDNA for human complement component C1s. The complete amino acid sequence.

The complete amino acid sequence (673 residues plus 15 residues of leader sequence) of human complement component C1s has been determined by nucleotide sequencing of cDNA clones from a human liver library probed with synthetic oligonucleotides. Much of the sequence is supported by independent amino acid sequence information. The cDNA sequence contains an anomalous "intron-like" sequence, including a stop codon, that can be discounted because of the amino acid sequence evidence. The N-terminal chain (422 residues) of C1s, like that of C1r with which it is broadly homologous, contains five domains: domains I and III are homologous to one another and to similar regions in C1r, domain II is homologous to the epidermal growth factor sequence found in C1r and several other proteins, and domains IV and V are homologous to one another and to the 60-residue repeating sequence found in C1r, C2, factor B, C4-binding protein and some apparently unrelated proteins. The sequence of the C-terminal chain (251 residues) agrees with that already established to be the "serine protease" domain of C1s.

Amino Acid Sequence↗

PubMed1986

The complete amino acid sequence of chicken skeletal-muscle enolase.

The complete amino acid sequence of chicken skeletal-muscle enolase, comprising 433 residues, was determined. The sequence was deduced by automated sequencing of hydroxylamine-cleavage, CNBr-cleavage, o-iodosobenzoic acid-cleavage, clostripain-digest and staphylococcal-proteinase-digest fragments. The presence of several acid-labile peptide bonds and the tenacious aggregation of most CNBr-cleavage fragments meant that a commonly used sequencing strategy involving initial CNBr cleavage was unproductive. Cleavage at the single Asn-Gly peptide bond with hydroxylamine proved to be particularly useful. Comparison of the sequence of chicken enolase with the two yeast enolase isoenzyme sequences shows that the enzyme is strongly conserved, with 60% of the residues identical. The histidine and arginine residues implicated as being important for the activity of yeast enolase are conserved in the chicken enzyme. Secondary-structure predictions are analysed in an accompanying paper [Sawyer, Fothergill-Gilmore & Russell (1986) Biochem. J. 236, 127-130].

Amino Acid Sequence↗