PubMed Health⌕ Search

Biomedical subjects

S Gough

Publications and source records attributed to S Gough.

14 recordsLinked to original sources
PubMed2001

Interplay between an AAA module and an integrin I domain may regulate the function of magnesium chelatase.

In chlorophyll biosynthesis, insertion of Mg(2+) into protoporphyrin IX is catalysed in an ATP-dependent reaction by a three-subunit (BchI, BchD and BchH) enzyme magnesium chelatase. In this work we present the three-dimensional structure of the ATP-binding subunit BchI. The structure has been solved by the multiple wavelength anomalous dispersion method and refined at 2.1 A resolution to the crystallographic R-factor of 22.2 % (R(free)=24.5 %). It belongs to the chaperone-like "ATPase associated with a variety of cellular activities" (AAA) family of ATPases, with a novel arrangement of domains: the C-terminal helical domain is located behind the nucleotide-binding site, while in other known AAA module structures it is located on the top. Examination by electron microscopy of BchI solutions in the presence of ATP demonstrated that BchI, like other AAA proteins, forms oligomeric ring structures. Analysis of the amino acid sequence of subunit BchD revealed an AAA module at the N-terminal portion of the sequence and an integrin I domain at the C terminus. An acidic, proline-rich region linking these two domains is suggested to contribute to the association of BchI and BchD by binding to a positively charged cleft at the surface of the nucleotide-binding domain of BchI. Analysis of the amino acid sequences of BchI and BchH revealed integrin I domain-binding sequence motifs. These are proposed to bind the integrin I domain of BchD during the functional cycle of magnesium chelatase, linking porphyrin metallation by BchH to ATP hydrolysis by BchI. An integrin I domain and an acidic and proline-rich region have been identified in subunit CobT of cobalt chelatase, clearly demonstrating its homology to BchD. These findings, for the first time, provide an insight into the subunit organisation of magnesium chelatase and the homologous colbalt chelatase.

Adenosine Triphosphatases↗
PubMed2000

The small GTPase RAC3 gene is located within chromosome band 17q25.3 outside and telomeric of a region commonly deleted in breast and ovarian tumours.

The closely related small GTP-binding proteins Rac1, Rac2, and Rac3 are part of a larger Rho subfamily of Ras proteins. Because disruption of Ras signaling pathways is relevant to the pathogenesis of a wide variety of cancers, it is important to clearly define the structural and functional characteristics of the participating proteins and their encoding genes. Rho subfamily members are involved in a range of signal transduction pathways relevant to cell growth, differentiation, motility, and stress, and Rac proteins are now recognised as a necessary component of Ras-mediated cellular transformation. We previously mapped RAC3 to chromosome band 17q23--> q25, a region that contains a number of candidate tumour suppressor genes. Because of its oncogenic potential, we have now further refined the location of this gene. Here we confirm that RAC3 maps to chromosome band 17q25.3 and further show that it maps some distance telomeric of a well-characterised minimal breast and ovarian candidate tumour suppressor gene region, BROV. The genomic structure of RAC3, including exon and intron boundaries, is also presented.

Amino Acid Sequence↗
PubMed1999

Cloning and characterization of a novel beta integrin-related cDNA coding for the protein TIED ("ten beta integrin EGF-like repeat domains") that maps to chromosome band 13q33: A divergent stand-alone integrin stalk structure.

Herein we describe the cDNA sequence of a novel human gene, ITGBL1, encoding a beta integrin-related protein termed TIED [for ten beta integrin epidermal growth factor (EGF)-like repeat domains]. Overlapping cDNA clones from fetal lung, HUVEC, and osteoblast cDNA libraries encode a sequence comprising a typical signal peptide, followed by a hydrophilic 471-amino-acid domain containing 10 tandem EGF-like repeats strikingly similar to those found in the cysteine-rich "stalk-like" structure of integrin beta subunits. The EGF-like repeats of TIED and beta integrins are unique in that they alternate in homology and possess two additional cysteines (eight in total) whose positions differ from those in the other eight-cysteine EGF-like domains of laminin, fibrillin, and the latent TGF-beta binding proteins. TIED mRNA transcripts of 2.8 kb were detected in aorta, thymus, and osteogenic sarcoma cells. The ITGBL1 gene was mapped to human chromosome 13, band 13q33. We suggest that ITGBL1 may be linked in some way with the evolution of the integrin beta subunits.

3' Untranslated Regions↗
PubMed1999

The integrin alpha10 subunit: expression pattern, partial gene structure, and chromosomal localization.

Herein we report the cloning of cDNAs and incompletely processed hnRNAs from endothelia and heart that encode the alpha10 subunit forming part of the novel collagen type II-binding integrin alpha10beta1 of chondrocytes. Analysis of hnRNA clones and reported expressed sequence tags revealed the positions of 17 putative intron-exon splice junctions shared with those of the p150,95 (ITGAX) gene. Human alpha10 transcripts of 5.4 and 1.8 kb were not restricted to chondrocytes but, instead, were widely expressed in a panel of 24 tissue types, where the highest expression was found in muscle and heart. The human alpha10 subunit gene (ITGA10) was localized to band q21 of chromosome 1.

Amino Acid Sequence↗
PubMed1996

Fermentation of molasses using a thermotolerant yeast, Kluyveromyces marxianus IMB3: simplex optimisation of media supplements.

The use of molasses as a substrate for ethanol production by the thermotolerant yeast Kluyveromyces marxianus var. marxianus was investigated at 45 degrees C. A maximum ethanol concentration of 7.4% (v/v) was produced from unsupplemented molasses at a concentration of 23% (v/v). The effect on ethanol production of increasing the sucrose concentration in 23% (v/v) molasses was determined. Increased sucrose concentration had a similar detrimental effect on the final ethanol produced as the increase in molasses concentration. This indicated that the effect may be due to increased osmotic activity as opposed to other components in the molasses. The optimum concentration of the supplements nitrogen, magnesium, potassium and fatty acid for maximum ethanol production rate was determined using the Nelder and Mead (Computer J 7:308-313, 1965) simplex optimisation method. The optimum concentration of the supplements were 0.576 g1(-1) magnesium sulphate, 0.288 g1(-1) potassium dihydrogen phosphate and 0.36% (v/v) linseed oil. Added nitrogen in the form of ammonium sulphate did not affect the ethanol production rate.

Culture Media↗
PubMed1996

Identification of trinucleotide repeat-containing genes in human pancreatic islets.

In the search for diabetes genes, the combined approaches of positional cloning with random markers and subsequent evaluation of candidate genes mapping to areas of interest will be increasingly used. For islet candidate genes of unknown function, expressed trinucleotide (triplet) repeats represent a unique subset. It is unlikely that abnormal expansion of expressed islet triplet repeats would be a major cause of diabetes, yet the triplet repeats are frequently polymorphic and can thus be used to map the genes in the human genome. In this study, a human islet cDNA library was screened with (CGG)7 and (CAG)7, and 23 triplet repeats were isolated. Sequencing revealed four known and six novel islet genes containing 4-15 triplet repeats. The four known cDNAs included ferritin, the major iron-binding protein in cells; HSGSA2R, a full-length clone of the alpha-subunit of the G-regulatory protein; HUMSATB1A, a DNA-binding protein expressed predominantly in thymus; and HUMPPA-PRO, a ribosomal protein. The triplet repeats in ferritin and HUMPPAPRO were found to be monomorphic. Characterization of the six unique novel expressed islet triplet cDNAs revealed that they were 0.6-1.5 kb in size, contained 4-15 triplet repeats, and were expressed in islets and all other tissues examined. Four of the novel clones, CGG-isl 10, CGG-isl 11, CAG-isl 6, and CAG-isl 7, were mapped to human chromosomes 19, 16, 12, and 3, respectively, via somatic cell hybrids. One islet cDNA, CAG-isl 7, contained a repeat that was highly polymorphic, with 14 alleles (4-18 triplets) in African-Americans (heterozygosity = 0.86) and 6 alleles (heterozygosity = 0.77) in whites. Northern analysis indicated that the mRNA was abundant in pancreatic islets. A putative full-length clone contained an open reading frame encoding 213 amino acids with a variable number of alanines (4-18) within the COOH-terminal. The gene was uniquely mapped with odds > 1,000:1 on chromosome 3p in Centre d'Etude du Polymorphisme Humain pedigrees. There were no differences in CAG-isl 7 allele frequencies between African-American patients with NIDDM (n = 108) and control subjects (n = 116), nor was expansion above 18 repeats noted. Linkage analysis in 14 nonglucokinase maturity-onset diabetes of the young pedigrees showed a cumulative logarithm of odds score of -33.19 at theta = 0.00. Abnormal expansion was not observed in 20 IDDM patients with one NIDDM parent. While these data suggest no major role for CAG-isl 7 in diabetes, at least four of the six novel islet triplet genes are coexpressed in pancreatic islets and neural tissue, and these genes can now be considered as candidates for diabetes and/or neuropsychiatric diseases.

Amino Acid Sequence↗
PubMed1994

The barley 60 kDa jasmonate-induced protein (JIP60) is a novel ribosome-inactivating protein.

The N-terminal region of a 60 kDa, jasmonate-induced protein of barley leaves (JIP60) is shown to be homologous to the catalytic domains of plant ribosome-inactivating proteins (RIP). Western blotting of leaf extracts and in vitro reconstitution experiments indicate that JIP60 is synthesized as a precursor which is processed in vivo. This is in keeping with in vitro translation experiments indicating that a deletion derivative of the N-terminal region, but not the putative precursor, strongly inhibits protein synthesis on reticulocyte ribosomes. The inhibition of ribosome function is associated with depurination of 26S rRNA, characteristic of plant RIPs. This indicates that JIP60 is a novel ribosome-inactivating protein requiring at least two processing events for full activation. JIP60 derivatives do not significantly inhibit in vitro protein synthesis on wheat germ ribosomes. These and other results suggest that JIP60 may be involved in plant defence.

Amino Acid Sequence↗
PubMed1992

Chloroplast tRNA(Asp): nucleotide sequence and variation of in vivo levels during plastid maturation.

Two chloroplast tRNA(Asp) species from barely were purified by chromatography on benzoylated DEAE-cellulose and sequenced. They differ in the modification at position 34, where queuosine (Q) is present in one of the species. The same chromatographic procedure yielded only one tRNA(Glu) species, corroborating the assumption that the same tRNA(Glu) species participates in both protein and chlorophyll biosynthesis. The level of tRNA(Glu) remains unchanged after light treatment of etiolated seedlings, whereas the amount of tRNA(Asp) decreases to about 50% relative to the level of dark-grown plants.

Base Sequence↗
PubMed1988

Protein biosynthesis in organelles requires misaminoacylation of tRNA.

In the course of our studies on transfer RNA involvement in chlorophyll biosynthesis, we have determined the structure of chloroplast glutamate tRNA species. Barley chloroplasts contain in addition to a tRNA(Glu) species at least two other glutamate-accepting tRNAs. We now show that the sequences of these tRNAs differ significantly: they are differentially modified forms of tRNA(Gln) (as judged by their UUG anticodon). These mischarged Glu-tRNA(Gln) species can be converted in crude chloroplast extracts to Gln-tRNA(Gln). This reaction requires a specific amidotransferase and glutamine or asparagine as amide donors. Aminoacylation studies show that chloroplasts, plant and animal mitochondria, as well as cyanobacteria, lack any detectable glutaminyl-tRNA synthetase activity. Therefore, the requirement for glutamine in protein synthesis in these cells and organelles is provided by the conversion of glutamate attached to an 'incorrectly' charged tRNA. A similar situation has been described for several species of Gram-positive bacteria. Thus, it appears that the occurrence of this pathway of Gln-tRNA(Gln) formation is widespread among organisms and is a function conserved during evolution. These findings raise questions about the origin of organelles and about the evolution of the mechanisms maintaining accuracy in protein biosynthesis.

Acylation↗
PubMed1988

Biosynthesis of delta-aminolevulinate in greening barley leaves. IX. Structure of the substrate, mode of gabaculine inhibition, and the catalytic mechanism of glutamate 1-semialdehyde aminotransferase.

Glutamic acid 1-semialdehyde hydrochloride was synthesized and purified. Its prior structural characterization was extended and confirmed by 1H NMR spectroscopy and chemical analyses. In aqueous solution at pH 1 to 2 glutamic acid 1-semialdehyde exists in a stable hydrated form, but at pH 8.0 it has a half-life of 3 to 4 min. Spontaneous degradation of the material at pH 8.0 generated some undefined condensation products, but coincidentally a significant amount isomerized to 5-aminolevulinate. At pH 6.8 to 7.0, glutamate 1-semialdehyde is sufficiently stable to permit routine and reproducible assay for glutamate 1-semialdehyde aminotransferase activity. Only about 20% of the enzyme extracted from chloroplasts was sensitive to inactivation by gabaculine with no pretreatment. However, when the enzyme was exposed to 5-aminolevulinate, levulinate or 4,5-dioxovalerate in the absence of glutamate 1-semialdehyde, it was completely inactivated by gabaculine; 4,6-dioxoheptanoate had no effect on the enzyme. These results lead to the hypothesis that the aminotransferase exists in the chloroplast in a complex with pyridoxamine phosphate, which must be converted to the pyridoxal form before it can form a stable adduct with gabaculine. We propose that the enzyme catalyzes the conversion of glutamate 1-semialdehyde to 5-aminolevulinate via 4,5-diaminovalerate.

Aminolevulinic Acid↗
PubMedDate not supplied

The RNA required in the first step of chlorophyll biosynthesis is a chloroplast glutamate tRNA.

A molecule of chlorophyll is synthesized from eight molecules of delta-aminolevulinate (DALA), the universal precursor of porphyrins. The light-regulated conversion of glutamate to delta-aminolevulinate in the stroma of greening plastids involves the reduction of glutamate to glutamate-1-semialdehyde and its subsequent transamination. The components performing this conversion have been isolated from barley and Chlamydomonas and separated into three fractions by serial affinity chromatography on Blue Sepharose and haem- or chlorophyllin-Sepharose. The complete reaction can be performed in vitro in a reconstituted assay by combining all three fractions. An RNA is the essential component of the chlorophyllin-Sepharose-bound fraction. By nucleotide sequence analysis, we have now identified this RNA as a chloroplast glutamate acceptor RNA. Glutamate attached by an aminoacyl bond to the 3'-terminal adenosine of this RNA is a substrate for the enzyme(s) which perform the subsequent reactions. This reaction represents a novel role for transfer RNA: participation in the metabolic conversion of its cognate amino acid into another metabolite of low relative molecular mass which subsequently is not used in peptide bond synthesis.

Aminolevulinic Acid↗