Biomedical subjects

Peter J Holt

Publications and source records attributed to Peter J Holt.

5 recordsLinked to original sources

PubMed2006

Projection structure of the membrane domain of Escherichia coli respiratory complex I at 8 A resolution.

Respiratory complex I (NADH:ubiquinone oxidoreductase) is an L-shaped multisubunit protein assembly consisting of a hydrophobic membrane arm and a hydrophilic peripheral arm. It catalyses the transfer of two electrons from NADH to quinone coupled to the translocation of four protons across the membrane. Although we have solved recently the crystal structure of the peripheral arm, the structure of the complete enzyme and the coupling mechanism are not yet known. The membrane domain of Escherichia coli complex I consists of seven different subunits with total molecular mass of 258 kDa. It is significantly more stable than the whole enzyme, which allowed us to obtain well-ordered two-dimensional crystals of the domain, belonging to the space group p22(1)2(1). Comparison of the projection map of negatively stained crystals with previously published low-resolution structures indicated that the characteristic curved shape of the membrane domain is remarkably well conserved between bacterial and mitochondrial enzymes, helping us to interpret projection maps in the context of the intact complex. Two pronounced stain-excluding densities at the distal end of the membrane domain are likely to represent the two large antiporter-like subunits NuoL and NuoM. Cryo-electron microscopy on frozen-hydrated crystals allowed us to calculate a projection map at 8 A resolution. About 60 transmembrane alpha-helices, both perpendicular to the membrane plane and tilted, are present within one membrane domain, which is consistent with secondary structure predictions. A possible binding site and access channel for quinone are found at the interface with the peripheral arm. Tentative assignment of individual subunits to the features of the map has been made. The location of subunits NuoL and NuoM at substantial distance from the peripheral arm, which contains all the redox centres of the complex, indicates that conformational changes are likely to play a role in the mechanism of coupling between electron transfer and proton pumping.

Cell Membrane↗

PubMed2006

Retroperitoneal anomalies in men with testicular germ cell tumours.

OBJECTIVES: To assess whether vascular and other retroperitoneal anomalies are more frequent during retroperitoneal lymph node dissection (RPLND) for metastatic testicular tumours (when retroperitoneal masses persist after chemotherapy) than would be expected, based on the initial observations from one centre with a large experience of RPLND in the UK. PATIENTS AND METHODS: A prospective series of 278 consecutive patients treated with RPLND for testicular tumours comprised the sample population. For each patient the presence or absence of four factors from the history was recorded. Each patient then underwent RPLND. During surgery, a template was constructed of the anatomy of the retroperitoneum and the information stored. Eight different retroperitoneal anatomical anomalies were identified in the sample population; the incidence of each was then compared with the largest available study of a normal population, and differences analysed statistically. RESULTS: Of the 278 patients who had RPLND, 55 had 59 anomalies (21%), found by history and as retroperitoneal vascular and urological anomalies; cryptorchidism was present in 7.6%, 9.5 times the incidence in the control population (P < 0.01). A left-sided inferior vena cava was present in 3.6% of patients, 21 times the incidence in the control population (P < 0.001); a retro-aortic left renal vein in 3.2%, four times that in the control population (P < 0.05); and ipsilateral renal agenesis had an incidence of 1% in the test population, 11 times greater than in the control population (P < 0.01). CONCLUSIONS: This prospective study of 278 RPLNDs provides evidence that some retroperitoneal anatomical anomalies are associated with testicular germ cell tumours. The link between maldescent and testicular tumours, rather than an isolated association, should be considered as part of a spectrum of retroperitoneal anomalies that occur in these men.

Cardiovascular Abnormalities↗

PubMed2004

Substrate-induced conformational change in bacterial complex I.

The mechanism coupling electron transfer and proton pumping in respiratory complex I (NADH-ubiquinone oxidoreductase) has not been established, but it has been suggested that it involves conformational changes. Here, the influence of substrates on the conformation of purified complex I from Escherichia coli was studied by cross-linking and electron microscopy. When a zero-length cross-linking reagent was used, the presence of NAD(P)H, in contrast to that of NAD+, prevented the formation of cross-links between the hydrophilic subunits of the complex, including NuoB, NuoI, and NuoCD. Comparisons using different cross-linkers suggested that NuoB, which is likely to coordinate the key iron-sulfur cluster N2, is the most mobile subunit. The presence of NAD(P)H led also to enhanced proteolysis of subunit NuoG. These data indicate that upon NAD(P)H binding, the peripheral arm of the complex adopts a more open conformation, with increased distances between subunits. Single particle analysis showed the nature of this conformational change. The enzyme retains its L-shape in the presence of NADH, but exhibits a significantly more open or expanded structure both in the peripheral arm and, unexpectedly, in the membrane domain also.

Electron Transport Complex I↗

PubMed2003

The location of NuoL and NuoM subunits in the membrane domain of the Escherichia coli complex I: implications for the mechanism of proton pumping.

The molecular organization of bacterial NADH: ubiquinone oxidoreductase (complex I or NDH-1) is not established, apart from a rough separation into dehydrogenase, connecting and membrane domains. In this work, complex I was purified from Escherichia coli and fragmented by replacing dodecylmaltoside with other detergents. Exchange into decyl maltoside led to the removal of the hydrophobic subunit NuoL from the otherwise intact complex. Diheptanoyl phosphocholine led to the loss of NuoL and NuoM subunits, whereas other subunits remained in the complex. The presence of N,N-dimethyldodecylamine N-oxide or Triton X-100 led to further disruption of the membrane domain into fragments containing NuoL/M/N, NuoA/K/N, and NuoH/J subunits. Among the hydrophilic subunits, NuoCD was most readily dissociated from the complex, whereas NuoB was partially dissociated from the peripheral arm assembly in N,N-dimethyldodecylamine N-oxide. A model of subunit arrangement in bacterial complex I based on these data is proposed. Subunits NuoL and NuoM, which are homologous to antiporters and are implicated in proton pumping, are located at the distal end of the membrane arm, spatially separated from the redox centers of the peripheral arm. This is consistent with proposals that the mechanism of proton pumping by complex I is likely to involve long range conformational changes.

Cell Membrane↗

PubMed2002

Melioidosis in the Torres Strait islands of far North Queensland.

During the six-year period from 1995 to 2000, 23 cases of melioidosis were diagnosed from the Torres Strait islands that lie between northern Queensland and Papua New Guinea. This represents an average annual incidence of 42.7 per 100,000 population, the highest documented to date in this region. This probably reflects the extremely high prevalence of diabetes, the high seasonal rainfall in the area, and the lifestyle of Torres Strait Islanders. The majority of patients (20 out of 23) acquired their disease in one of the more remote outer island indigenous communities. Most patients presented with a community-acquired pneumonia or with deep seated abscesses. One patient presented with the first case of suppurative parotitis due to melioidosis recorded in Australia. Diabetes was the overwhelming risk factor, being present in over three-quarters of all cases. Five patients (22%) died. Strategies to try to minimise illness and death due to melioidosis in the Torres Strait are discussed.

Adult↗