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P Metcalf

Publications and source records attributed to P Metcalf.

At least 19 recordsLinked to original sources
PubMed2003

Universality and critical behavior at the Mott transition.

We report conductivity measurements of Cr-doped V2O3 using a variable pressure technique. The critical behavior of the conductivity near the Mott insulator to metal critical endpoint is investigated in detail as a function of pressure and temperature. The critical exponents are determined, as well as the scaling function associated with the equation of state. The universal properties of a liquid-gas transition are found. This is potentially a generic description of the Mott critical endpoint in correlated electron materials.

Journal Article↗
PubMed2003

Prominent quasiparticle peak in the photoemission spectrum of the metallic phase of V2O3.

We present the first observation of a prominent quasiparticle peak in the photoemission spectrum of the metallic phase of V2O3 and report new spectral calculations that combine the local-density approximation with the dynamical mean-field theory (using quantum Monte Carlo simulations) to show the development of such a distinct peak with decreasing temperature. The experimental peak width and weight are significantly larger than in the theory.

Journal Article↗
PubMed2003

Development of a highly sensitive screen for influenza A in guano and its application in the search for ancient RNA preserved under Antarctic Adelie penguin colonies.

We have developed a reverse transcriptase polymerase chain reaction (RT-PCR)-based assay to detect influenza A in guano samples as part of our program to investigate ancient viral RNA from under Antarctic Adelie penguin (Pygoscelis adeliae) colonies. Of five extraction protocols tested (RNeasy, GTC TRIZOL, GTC Silica, Rnaid, and AGPC), AGPC proved to be the most consistent and sensitive to low concentrations of influenza, but further purification with commercial viral nucleic acid spin filter system was still required to remove remaining PCR inhibitors. RT-PCR was then performed on the eluent and 650 bases of the M1 gene were amplified. The assay was found to be able to detect as little as 100 microl of 0.1 hemagglutination units (HU)/ml influenza.

Animals↗
PubMed2001

LISA: an intranet-based flexible database for protein crystallography project management.

The increase in the number of projects carried out in protein crystallography laboratories has emphasized the need for effective management of project information and data. To meet this need, a flexible web-accessible database for protein crystallography project management (LISA) has been developed using the open-source software MySQL and PHP4. The database contains information about all aspects of structure-determination projects, including primer and plasmid sequences, protein expression, purification and crystallization results, structure coordinate files and resultant publications. The database web pages include links to relevant servers and contain, in addition, tools for processing stored information. The software package is freely available.

Crystallography↗
PubMed2001

DsbC activation by the N-terminal domain of DsbD.

The correct formation of disulfide bonds in the periplasm of Escherichia coli involves Dsb proteins, including two related periplasmic disulfide-bond isomerases, DsbC and DsbG. DsbD is a membrane protein required to maintain the functional oxidation state of DsbC and DsbG. In this work, purified proteins were used to investigate the interaction between DsbD and DsbC. A 131-residue N-terminal fragment of DsbD (DsbDalpha) was expressed and purified and shown to form a functional folded domain. Gel filtration results indicate that DsbDalpha is monomeric. DsbDalpha was shown to interact directly with and to reduce the DsbC dimer, thus increasing the isomerase activity of DsbC. The DsbC-DsbDalpha complex was characterized, and formation of the complex was shown to require the N-terminal dimerization domain of DsbC. These results demonstrate that DsbD interacts directly with full-length DsbC and imply that no other periplasmic components are required to maintain DsbC in the functional reduced state.

Bacterial Proteins↗
PubMed2001

Turning a disulfide isomerase into an oxidase: DsbC mutants that imitate DsbA.

There are two distinct pathways for disulfide formation in prokaryotes. The DsbA-DsbB pathway introduces disulfide bonds de novo, while the DsbC-DsbD pathway functions to isomerize disulfides. One of the key questions in disulfide biology is how the isomerase pathway is kept separate from the oxidase pathway in vivo. Cross-talk between these two systems would be mutually destructive. To force communication between these two systems we have selected dsbC mutants that complement a dsbA null mutation. In these mutants, DsbC is present as a monomer as compared with dimeric wild-type DsbC. Based on these findings we rationally designed DsbC mutants in the dimerization domain. All of these mutants are able to rescue the dsbA null phenotype. Rescue depends on the presence of DsbB, the native re-oxidant of DsbA, both in vivo and in vitro. Our results suggest that dimerization acts to protect DsbC's active sites from DsbB-mediated oxidation. These results explain how oxidative and reductive pathways can co-exist in the periplasm of Escherichia coli.

Bacterial Proteins↗
PubMed2001

Crystallization and initial crystallographic analysis of the disulfide bond isomerase DsbC in complex with the alpha domain of the electron transporter DsbD.

The protein disulfide bond isomerase DsbC catalyzes the rearrangement of incorrect disulfide bonds during oxidative protein folding in the periplasm of Escherichia coli. The active site cysteines of DsbC are maintained in the active reduced form by the transmembrane electron transporter DsbD. DsbD obtains electrons from the cytoplasm, transports them across the inner membrane, and passes them onto periplasmic substrates, such as DsbC. The electron transport process involves several thiol disulfide exchange reactions between different classes of thiol oxidoreductase. We were able to trap the final electron transport reaction using active site mutants yielding a stable DsbC-DsbDalpha complex. This disulfide cross-linked complex was purified to homogeneity and crystallized. Dehydration of the tetragonal crystals changed the unit cell dimensions from a approximately b = 73 A, c = 267.5 A to a = b = 68.9 A, c = 230.3 A, reducing the cell volume by 23% and the solvent content from 55 to 41%. Crystal dehydration and cryo-cooling improved the diffraction quality of the crystals from 7 to 2.3 A resolution.

Crystallization↗
PubMed2000

Prevalence of iron deficiency in Auckland high school students.

AIMS: To determine the frequency of iron deficiency and anaemia in high school students. METHOD: The survey was carried out at eight Auckland high schools with a high proportion (> or =15%) of Pacific Islands students. All students in Forms 5-7 at these schools were invited to participate, and 1644 students (Pacific Island 765, Asian 350, European 295, Maori 234) had iron assessments (response rate 61%). Iron deficiency was defined as any two (or more) of the following, three: serum ferritin <12 microg/L, iron saturation <14%, or red cell distribution width >14.5%. Anaemia was defined as haemoglobin <120 g/L for females and <130 g/L for males. RESULTS: Iron deficiency and anaemia were each ten times more common in girls (18.3% and 11.5%, respectively) than boys (1.5% and 1.4%). In females, iron deficiency was two to three times more common in Maori (25.6%), Pacific Islanders (20.9%) and Asians (15.4%) compared with Europeans (8.3 %), while anaemia was three to four times more common in Asians (15.9%), Pacific Islanders (12.1%) and Maori (11.2%) compared with Europeans (4.2%). Iron deficiency and anaemia prevalences were inversely associated with aerobic fitness, but not with age or years since menarche. CONCLUSION: Prevalences of iron deficiency and anaemia are high in non-European female adolescents in Auckland, for reasons currently unknown.

Adolescent↗
PubMed2000

Cardiovascular risk factors levels of Pacific people in a New Zealand multicultural workforce.

AIMS: To compare cardiovascular risk factors among the major Pacific Island communities participating in a New Zealand multicultural workforce survey. METHOD: There were 650 employed Pacific Island participants (Samoan 357, Cook Islands 177, Tongan 71, Niuean 45), aged 40-65 years, who were interviewed in a work-based, cross-sectional survey. During an oral glucose tolerance test, blood samples were collected for determination of blood glucose and serum lipids. Participants provided information on smoking and leisure time physical activity. Blood pressure, weight and height were measured and body mass index calculated. Ten-year risk of cardiovascular disease was calculated using equations from the Framingham study. RESULTS: Among men, their ten-year risk of a cardiovascular event was similar for the four communities compared (range 11.5% to 13.2%). However, individual risk factors did vary between the ethnic groups with Cook Island men having significantly higher total cholesterol, blood pressure and urinary microalbumin than other Pacific Island ethnic groups, while Tongan men were more likely to smoke and had lower HDL levels than other groups. Among women, Samoan and Cook Island participants had significantly higher ten-year cardiovascular risk scores (5.7%) than Niuean (4.4%) and Tongan (3.7%), due primarily to elevated total cholesterol levels. CONCLUSION: Cardiovascular risk factor levels vary between Pacific Islands communities in New Zealand. Targeted interventions to specific Pacific communities may be more beneficial than the current homogeneous prevention strategy applied to all communities.

Adult↗
PubMed2000

Crystal structure of the protein disulfide bond isomerase, DsbC, from Escherichia coli.

DsbC is one of five Escherichia coli proteins required for disulfide bond formation and is thought to function as a disulfide bond isomerase during oxidative protein folding in the periplasm. DsbC is a 2 x 23 kDa homodimer and has both protein disulfide isomerase and chaperone activity. We report the 1.9 A resolution crystal structure of oxidized DsbC where both Cys-X-X-Cys active sites form disulfide bonds. The molecule consists of separate thioredoxin-like domains joined via hinged linker helices to an N-terminal dimerization domain. The hinges allow relative movement of the active sites, and a broad uncharged cleft between them may be involved in peptide binding and DsbC foldase activities.

Amino Acid Sequence↗
PubMed1998

The crystal structure of the Leishmania major surface proteinase leishmanolysin (gp63).

BACKGROUND: Despite their medical importance, there is little available structural information for the surface antigens of infectious protozoa. Diseases caused by the protozoan parasite Leishmania are common in many developing countries. Human infection occurs during the bite of infected sandfilies, when Leishmania promastigote cells from the insect gut enter the bloodstream. Promastigotes in the blood parasitize macrophages, often causing serious disease. Leishmanolysin is the predominant protein surface antigen of promastigotes, and is assumed to have a key role during infection. Leishmanolysin is a membrane-bound zinc proteinase, active in situ. Similar molecules exist in other trypanomastid protozoa. RESULTS: Two crystal forms of leishmanolysin were obtained from protein purified from promastigote membranes. A single lead derivative in both crystal forms was used to solve the structure. The structure reveals three domains, two of which have novel folds. The N-terminal domain has a similar structure to the catalytic modules of zinc proteinases. The structure clearly shows that leishmanolysin is a member of the metzincin class of zinc proteinases. CONCLUSIONS: The unexpected metzincin features of the leishmanolysin structure suggest that the metzincin fold may be more widespread than indicated by sequence homologies amongst existing metzincin zinc proteinases. The similarity of the active-site structure to previously well characterized metzincin class zinc proteinases should aid the development of specific inhibitors. These inhibitors might be used to determine the function of leishmanolysin in the insect and during mammalian infection, and may aid the development of drugs for human leishmaniasis.

Amino Acid Sequence↗
PubMed1997

Rab7: NMR and kinetics analysis of intact and C-terminal truncated constructs.

Rab proteins are a family of approximately 25kD ras-related GTPases which are associated with distinct intracellular membranes where they control vesicle traffic between intracellular compartments. The late-endosomal rab protein rab7(1-207), (lacking only the C-terminal lipids of the native molecule) and three C-terminal truncated constructs rab7(1-202), rab7(1-197) and rab7(1-182) were purified using an E. coli expression system. The C-terminal tail region of rab proteins is of special interest because it is thought to target rab proteins to particular intracellular membranes. A comparison of TOCSY-NMR spectra from intact rab7(1-207) and the tail-less construct rab7(1-182) suggested that much of the C-terminal tail is flexible in solution. The GTP hydrolysis, and GDP association and dissociation rates for all the truncated and intact constructs were similar, showing that the tail region of rab7(1-207) has little influence on the hydrolysis and exchange rates of the nucleotide.

GTP-Binding Proteins↗
PubMed1997

Rab7: crystallization of intact and C-terminal truncated constructs complexed with GDP and GppNHp.

The GTP/GDP conformational switch of members of the rab family of ras-related GTP-ases control specific intracellular vesicle transport pathways. We report the crystallization of the late-endosomal rab protein rab7, in both GTP and GDP conformations. X-ray data from crystals of rab7(1-207) GppNHp (i.e., intact rab7, without C-terminal bound lipid, complexed with a non-hydrolysable GTP analog), rab7(1-197)GppNHp and rab7(1-197)GDP were collected to 1.9A (0 degree C), 1.76A (100 degrees K) and 1.75A (100 degrees K) respectively. Rab7-GDP crystals diffract to at least 1.35A.

Crystallography, X-Ray↗
PubMed1997

Reproducibility and validity of a food frequency questionnaire in European and Polynesian New Zealanders.

The reproducibility and validity of a self-administered 142-item food-frequency questionnaire (FFQ) was assessed in a population comprising 124 European and 52 Polynesian (17 Maori and 35 Pacific Island) New Zealanders aged 40-65 years. Reproducibility correlation coefficients, determined by administration of the same questionnaire on two occasions 3 years apart, were higher in European than Maori and Pacific Island participants, ranging from 0.47 to 0.87 in Europeans (median 0.66) and from 0.41 to 0.79 in Maori and Pacific Island people (median 0.44). In general, there were no significant differences in mean nutrient intakes calculated from the two FFQs by Europeans or Maori and Pacific Island participants despite their cultural and language differences. When the FFQ was compared with a 3-day food diary in a subsample of 101 Europeans, 15 Maori and 22 Pacific Islanders, the validity was good for most nutrients, with overestimation of a few nutrients in each ethnic group. Correlation coefficients between the 3-day food diary and FFQ ranged from 0.41 to 0.81 in Europeans (median 0.48) and from 0.36 to 0.56 in Maori and Pacific Island people (median 0.55). Ratios of energy intake to resting metabolic rate suggested that Maori and Pacific Island people were more likely to underestimate their habitual energy intake by the 3-day diet diary method compared to Europeans, but that Europeans were more likely to underestimate total energy intake by the food frequency method and Pacific Island participants to overestimate it. Obese Europeans and Maori were more likely to under-report dietary intakes by the 3-day diary method. We conclude that our FFQ performed better in European than Maori and Pacific Island participants.

Adult↗
PubMed1997

Risk factors differ for carotid artery plaque with and without acoustic shadowing. Atherosclerosis Risk in Communities Study Investigators.

To investigate the association of gender, ethnicity, and several cardiovascular risk factors with carotid artery plaque and plaque with acoustic shadowing in a population-based sample, high-resolution B-mode ultrasonography was used to characterize lesions in the common and internal carotid arteries, and at the carotid bifurcation in 12,796 US men and women, aged 45 to 64 years, participating in the Atherosclerosis Risk in Communities Study (ARIC) baseline survey. In multiple logistic regression analyses, male gender (odds ratio and 95% confidence interval: 1.52 [1.39-1.67]) and increased total (1.47 [1.32-1.63]) and low-density-lipoprotein cholesterol (1.49 [1.34-1.65]) levels were statistically significantly associated only with the presence of plaque. In contradistinction, smoking (2.22 [1.79-2.75]) and hypertension (1.54 [1.30-1.82]) were additionally associated with acoustic shadowing. Hyperfibrinogenemia (1.33 [1.12-1.59]) was associated only with lesions accompanied by acoustic shadowing. While ethnicity associations with plaque alone varied across the artery segments, among those with plaque, being white was uniformly associated with acoustic shadowing. After multivariable adjustment, high-density-lipoprotein cholesterol was not associated with either manifestation of atherosclerosis. In conclusion, differences were seen in the associations of established cardiovascular risk factors with discretely characterized carotid artery plaque lesions, according to the presence or absence of acoustic shadowing suggestive of mineralization of plaque.

Carotid Artery, Common↗