How the structure of the large subunit controls function in an oxygen-tolerant [NiFe]-hydrogenase

Salmonella enterica is an opportunistic pathogen that produces a [NiFe]-hydrogenase under aerobic conditions. In the present study, genetic engineering approaches were used to facilitate isolation of this enzyme, termed Hyd-5. The crystal structure was determined to a resolution of 3.2 Å and the hydro-genase was observed to comprise associated large and small subunits. The structure indicated that His(229) from the large subunit was close to the proximal [4Fe–3S] cluster in the small subunit. In addition, His(229) was observed to lie close to a buried glutamic acid (Glu(73)), which is conserved in oxygen-tolerant hydrogenases. His(229) and Glu(73) of the Hyd-5 large subunit were found to be important in both hydrogen oxidation activity and the oxygen-tolerance mechanism. Substitution of His(229) or Glu(73) with alanine led to a loss in the ability of Hyd-5 to oxidize hydrogen in air. Furthermore, the H229A variant was found to have lost the overpotential requirement for activity that is always observed with oxygen-tolerant [NiFe]-hydrogenases. It is possible that His(229) has a role in stabilizing the super-oxidized form of the proximal cluster in the presence of oxygen, and it is proposed that Glu(73)could play a supporting role in fine-tuning the chemistry of His(229) to enable this function

Anticoagulation in cancer-associated thromboembolism with thrombocytopenia: a prospective, multi-center cohort study

Venous thromboembolism (VTE) with concurrent thrombocytopenia is frequently encountered in patients with cancer. Therapeutic anticoagulation in the setting of thrombocytopenia is associated with a high risk of hemorrhage. Retrospective analyses suggest the utility of modified-dose anticoagulation in this population. To assess the incidence of hemorrhage or thrombosis according to anticoagulation strategy, we performed a prospective, multi-center, observational study. Patients with active malignancy, acute VTE, and concurrent thrombocytopenia (platelet count \u3c 100,000/µL) were enrolled. The cumulative incidences of hemorrhage or recurrent VTE were determined considering death as a competing risk. Primary outcomes were centrally adjudicated and comparisons made according to initial treatment with full-dose or modified-dose anticoagulation. A total of 121 patients were enrolled at six hospitals. Seventy-five patients were initially treated with full-dose anticoagulation (62%), 33 (27%) with modified-dose anticoagulation, while 13 (11%) received no anticoagulation. Most patients who received modified-dose anticoagulation had a hematologic malignancy (31 of 33, 94%) and an acute DVT (28 of 33, 85%). In patients who initially received full-dose anticoagulation, the cumulative incidence of major hemorrhage at 60 days was 12.8% (95% CI, 4.9-20.8%) and 6.6% (95% CI, 2.4-15.7%) in those who received modified-dose anticoagulation (Fine-Gray HR 2.18, 95% CI 1.21-3.93). The cumulative incidence of recurrent VTE at 60 days in patients who initially received full-dose anticoagulation was 5.6% (95% CI, 0.2-11%) and 0% in patients who received modified-dose anticoagulation. In conclusion, modified-dose anticoagulation appears to be a safe alternative to therapeutic anticoagulation in patients with cancer who develop DVT in the setting of thrombocytopenia