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Biomedical subjects

A Bevan

Publications and source records attributed to A Bevan.

15 recordsLinked to original sources
PubMed2003

To play 'B' but not to say 'B': selective loss of letter names.

This paper is the first report of an aphasic patient (GT) who shows a selective impairment in naming musical notes and letters in the context of preserved instrumental reading of notes. The ability to orally name notes (which are given the letter names A-G in English) and to play notes from a spoken note name was severely impaired. By contrast, instrumental sightreading and matching of written letters and single notes were both well preserved. This complex pattern of impairments can be explained in terms of a selective deficit in the letter name system.

Adult↗
PubMed2001

GSA11 encodes a unique 208-kDa protein required for pexophagy and autophagy in Pichia pastoris.

Cells are capable of adapting to changes in their environment by synthesizing needed proteins and degrading superfluous ones. Pichia pastoris synthesizes peroxisomal enzymes to grow in methanol medium. Upon adapting from methanol medium to one containing glucose, this yeast rapidly and selectively degrades peroxisomes by an autophagic process referred to as pexophagy. In this study, we have utilized a novel approach to identify genes required for this degradative pathway. Our approach involves the random integration of a vector containing the Zeocin resistance gene into the yeast genome by restriction enzyme-mediated integration. Cells unable to degrade peroxisomes during glucose adaptation were isolated, and the genes that were disrupted by the insertion of the vector were determined by sequencing. By using this approach, we have identified a number of genes required for glucose-induced selective autophagy of peroxisomes (GSA genes). We report here the characterization of Gsa11, a unique 208-kDa protein. We found that this protein is required for glucose-induced pexophagy and starvation-induced autophagy. Gsa11 is a cytosolic protein that becomes associated with one or more structures situated near the vacuole during glucose adaptation. The punctate localization of Gsa11 was not observed in gsa10, gsa12, gsa14, and gsa19 mutants. We have previously shown that Gsa9 appears to relocate from a compartment at the vacuole surface to regions between the vacuole and the peroxisomes being sequestered. In the gsa11 mutants, the vacuole only partially surrounded the peroxisomes, but Gsa9 was still distributed around the peroxisome cluster. This suggests that Gsa9 binds to the peroxisomes independent of the vacuole. The data also indicate that Gsa11 is not necessary for Gsa9 to interact with peroxisomes but acts at an intermediate event required for the vacuole to engulf the peroxisomes.

Amino Acid Sequence↗
PubMed2001

Cvt18/Gsa12 is required for cytoplasm-to-vacuole transport, pexophagy, and autophagy in Saccharomyces cerevisiae and Pichia pastoris.

Eukaryotic cells have the ability to degrade proteins and organelles by selective and nonselective modes of micro- and macroautophagy. In addition, there exist both constitutive and regulated forms of autophagy. For example, pexophagy is a selective process for the regulated degradation of peroxisomes by autophagy. Our studies have shown that the differing pathways of autophagy have many molecular events in common. In this article, we have identified a new member in the family of autophagy genes. GSA12 in Pichia pastoris and its Saccharomyces cerevisiae counterpart, CVT18, encode a soluble protein with two WD40 domains. We have shown that these proteins are required for pexophagy and autophagy in P. pastoris and the Cvt pathway, autophagy, and pexophagy in S. cerevisiae. In P. pastoris, Gsa12 appears to be required for an early event in pexophagy. That is, the involution of the vacuole or extension of vacuole arms to engulf the peroxisomes does not occur in the gsa12 mutant. Consistent with its role in vacuole engulfment, we have found that this cytosolic protein is also localized to the vacuole surface. Similarly, Cvt18 displays a subcellular localization that distinguishes it from the characterized proteins required for cytoplasm-to-vacuole delivery pathways.

Amino Acid Sequence↗
PubMed1998

Quantitative assessment of enzyme specificity in vivo: P2 recognition by Kex2 protease defined in a genetic system.

The specificity of the yeast proprotein-processing Kex2 protease was examined in vivo by using a sensitive, quantitative assay. A truncated prepro-alpha-factor gene encoding an alpha-factor precursor with a single alpha-factor repeat was constructed with restriction sites for cassette mutagenesis flanking the single Kex2 cleavage site (-SLDKR downward arrowEAEA-). All of the 19 substitutions for the Lys (P2) residue in the cleavage site were made. The wild-type and mutant precursors were expressed in a yeast strain lacking the chromosomal genes encoding Kex2 and prepro-alpha-factor. Cleavage of the 20 sites by Kex2, expressed at the wild-type level, was assessed by using a quantitative-mating assay with an effective range greater than six orders of magnitude. All substitutions for Lys at P2 decreased mating, from 2-fold for Arg to >10(6)-fold for Trp. Eviction of the Kex2-encoding plasmid indicated that cleavage of mutant sites by other cellular proteases was not a complicating factor. Mating efficiencies of strains expressing the mutant precursors correlated well with the specificity (kcat/KM) of purified Kex2 for comparable model peptide substrates, validating the in vivo approach as a quantitative method. The results support the conclusion that KM, which is heavily influenced by the nature of the P2 residue, is a major determinant of cleavage efficiency in vivo. P2 preference followed the rank order: Lys > Arg > Thr > Pro > Glu > Ile > Ser > Ala > Asn > Val > Cys > AsP > Gln > Gly > His > Met > Leu > Tyr > Phe > Trp.

Amino Acid Sequence↗
PubMed1993

One-step site-directed mutagenesis of the Kex2 protease oxyanion hole.

BACKGROUND: Members of the subtilisin family of serine proteases usually have a conserved asparagine residue that stabilizes the oxyanion transition state of peptide-bond hydrolysis. Yeast Kex2 protease is a member of the subtilisin family that differs from the degradative subtilisin proteases in its high substrate specificity, it processes pro-alpha-factor, the precursor of the alpha-factor mating pheromone of yeast, and also removes the pro-peptide from its own precursor by an intramolecular cleavage reaction. Curiously, the mammalian protease PC2, a Kex2 homolog that is likely to be required for pro-insulin processing, has an aspartate in place of asparagine at the 'oxyanion hole'. RESULTS: We have tested the effect of making substitutions of the conserved oxyanion-hole asparagine (Asn 314) of the Kex2 protease. To do this, we have developed a rapid method of site-directed mutagenesis, involving homologous recombination of a polymerase chain reaction product in yeast. Using this method, we have substituted alanine or aspartate for Asn 314 in a form of Kex2 engineered for secretion. Transformants expressing the two mutant enzymes could be identified by failure either to produce mature alpha-factor or to mate. The Ala 314 enzyme was unstable but the Asp 314 enzyme accumulated to a high level, so that it could be purified and its activity towards various substrates tested in vitro. We found that, with three peptides that are good substrates of wild-type Kex2, the k(cal) of the Asp 314 enzyme was reduced approximately 4500-fold and its K(M) approximately 4-fold, relative to the wild-type enzyme. For the peptide substrate corresponding to the cleavage site of pro-alpha-factor, however, k(cat) of the Asp 314 enzyme was reduced only 125-fold, while the K(m) was increased 3-fold. Despite its reduced catalytic activity, however, processing of the mutant enzyme in vivo - by the intramolecular cleavage that removes its amino-terminal pro-domain - occurs at an unchanged rate. CONCLUSIONS: The effects of the Asn 314-Asp substitution reveal contributions to the reaction specificity of the Kex2 protease of substrate residues amino-terminal to the pair of basic residues at the cleavage site. Aspartate at the oxyanion hole appears to confer k(caf) discrimination between substrates by raising the energy barrier for productive substrate binding: this may have implications for pro-insulin processing by the PC2 protease, which has an aspartate at the equivalent position. The rate of intramolecular cleavage of pro-Kex2 may be limited by a step other than catalysis, presumably protein folding.

Journal Article↗
PubMed1992

[Health effects of chronic exposure to tobacco smoke on a non-smoker population].

A study devised to evaluate the effects of chronic exposure to tobacco smoke on the health of a population of non-smokers was conducted in a prison. Fourteen volunteers among male, non-smoking prisoners in good health and without history of lung disease were put for thirty days in a cell that was already occupied by three smokers. These subjects were examined on arrival and on the 30th day of their imprisonment. The examination included filling a questionnaire concerning daily habits and food, respiratory function tests, measurement of CO in the expired air, measurement of nicotine, cotinine, thiocyanates and cadmium concentrations in blood and in urine, and measurement of mutagenic substances excreted. The purpose of the study was to detect possible changes in the variables tested between the first and last days of confinement. No significant difference could be demonstrated within this lapse of time. These results are in agreement with the data available in the literature. In the present state of our knowledge, it is difficult to find evidence of a biological impact, notably on the concentrations of the specific indicators nicotine and cotinine, in subjects passively exposed to tobacco smoke.

Adult↗
PubMed1990

Immunotherapy of tree pollen allergy with a modified alginate conjugated birch pollen extract compared to an aluminium adsorbed extract.

The safety and efficacy of two birch pollen extracts, one chemically conjugated to alginate (Anjuvac) the other adsorbed to aluminium hydroxide (Alutard), were investigated in an open multicentre comparative study of 63 birch pollen allergic patients. Both extracts decreased the nasal symptoms during the birch pollen season. The changes in specific IgE and IgG were much the same in both treatment groups. The adverse reactions recorded were mild in both groups, but more frequent in the Anjuvac group, probably because of a more aggressive dose schedule though there were twice as many asthmatics in the Anjuvac group. The two investigated allergen extracts were useful alternatives for immunotherapy.

Adolescent↗
PubMed1989

Late renal failure due to prostatic outflow obstruction: a preventable disease.

Nineteen patients presenting with late renal failure due to prostatic outflow obstruction (mean age 68.7 years; mean serum creatinine concentration 1158 mumol/l) were identified from the admission records of two renal units. As late renal failure secondary to prostatic enlargement is preventable case records were analysed retrospectively in an attempt to identify aspects of management in which preventive efforts might be of value. Delays in referral were common, with a mean of 2.8 years between the onset of prostatic symptoms and time of referral, six patients being referred who had had symptoms for more than three years. Four of five patients who had had a prostatectomy were known to be in renal failure at the time of operation but were not referred until 2-13 years later, when prostatic symptoms had recurred and there was evidence of progressive nephropathy with dilatation of the upper urinary tract. Two patients died on admission and eight (47% of survivors) required long term dialysis, most patients (80%) requiring some dialysis support during the initial period. These findings suggest that progressive nephropathy caused by prostatic outflow obstruction might, in part, be averted by more adequate screening of renal function in men with untreated prostatism and closer follow up of patients with uraemia at the time of prostatectomy.

Aged↗
PubMed1980

Cytochemistry of human T-cell subpopulations.

Acid phosphatase and esterase cytochemistry performed on purified normal human T-cell populations showed that both methods produced distinctive localized dot patterns of reactivity in 60-70% of cells. By examination of rosette preparations formed with ox erythrocytes coated with IgM (EAM), with IgG (EAG), or anti-human kappa and lambda light chains, it was shown that this pattern of reactivity was largely restricted to small T lymphocytes possessing receptors for the Fc of IgM (T mu cells). In addition, both B lymphocytes and T cells with receptors for the Fc of IgG (T gamma cells) were larger lymphocytes with more abundant cytoplasm and usually displayed scattered granular acid phosphatase activity; in esterase preparations both cell types were either negative or possessed similar scattered granular positivity. As compared with T mu cells, T gamma cells were seen to form loose spontaneous rosettes with sheep erythrocytes. Combined esterase and acid phosphatase staining showed that both enzyme activities in the T mu cells are localized in the same area, and ultrastructural acid phosphatase cytochemistry established that this was in distinctive lysosomal structures. T mu staining by both esterase and acid phosphatase cytochemistry was greatly reduced after rosetting with EAG, but not after rosette formation with EAM or sheep erythrocytes.

Acid Phosphatase↗
PubMed1979

Typical hairy-cell leukaemia with IgGk paraproteinaemia.

A case of hairy-cell leukaemia (HCL) with IgG(k) paraprotein is described. The typical clinico-pathological features of the patient are stressed, and it is shown that the hairy cells (HCs) were producing and secreting IgGk. The case is placed in a more general context by the demonstration that HCs from other typical cases of HCL produce and secrete IgG. These findings conclusively demonstrate that HCL is a B-cell disease.

Aged↗
PubMed1976

Nonmediated use of MEDLINE and TOXLINE by pathologists and pharmacists.

Pathologists and pharmacists have used terminals in their departmental areas successfully to perform searches on MEDLINE and TOXLINE, during the period from fall 1974 through August 1975; MEDLINE has been used more than TOXLINE. In the Department of Pathology at the University of Maryland Health Sciences Center, the annual rate of combined mediated and nonmediated use of MEDLINE increased from 142 search sessions to 432, over half of the identified use being by three individuals. About half of the total potential users from each group tried MEDLINE or TOXLINE at least once. Nine pathologists and seven pharmacists used MEDLINE five or more times. Five of the individuals in each group were "intensive" users, who concentrated more than half of their sessions within two months. Vocabulary experience and systems problems are touched on. Most individuals learned to use the systems from one another or in individual sessions with the authors, although a twenty-five page "minimanual" has also been used by a limited group.

Information Systems↗