Copper Centers in the Cryo-EM Structure of Particulate Methane Monooxygenase Reveal the Catalytic Machinery of Methane Oxidation.

The particulate methane monooxygenase (pMMO) is the first enzyme in the C1 metabolic pathway in methanotrophic bacteria. As this enzyme converts methane into methanol efficiently near room temperature, it has become the paradigm for developing an understanding of this difficult C1 chemistry. pMMO is a membrane-bound protein with three subunits (PmoB, PmoA, and PmoC) and 12-14 coppers distributed among different sites. X-ray crystal structures that have revealed only three mononuclear coppers at three sites have neither disclosed the location of the active site nor the catalytic mechanism of the enzyme. Here we report a cyro-EM structure of holo-pMMO from Methylococcus capsulatus (Bath) at 2.5 Å, and develop quantitative electrostatic-potential profiling to scrutinize the nonprotein densities for signatures of the copper cofactors. Our results confirm a mononuclear CuI at the A site, resolve two CuIs at the B site, and uncover additional CuI clusters at the PmoA/PmoC interface within the membrane (D site) and in the water-exposed C-terminal subdomain of the PmoB (E clusters). These findings complete the minimal set of copper factors required for catalytic turnover of pMMO, offering a glimpse of the catalytic machinery for methane oxidation according to the chemical principles underlying the mechanism proposed earlier.

Septicemia in adults: II. Factors in prognosis.

Over the period of 2 months between October and November, 1987, 190 episodes of septicemia in adults were monitored at Veterans General Hospital-Taipei. The most common causative microorganisms were Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus. The most frequent sources of infection came from intra-abdominal (gastro-intestinal as well as hepato-biliary), urinary and respiratory tract. Its overall mortality was 34.7%. Factors associated with a higher mortality from septicemia were old age, rapidly fatal underlying disease, hospital acquired infection, hypothermia, hypotension/shock, high-risk source of infection (from respiratory tract, skin/soft tissue, surgical wound or other unknown source), high-risk microorganisms (Candida species, Ps. aeruginosa or K. Pneumoniae) and inappropriate antimicrobial therapy. Identification of these factors may help early correction of reversible factors and improve its prognosis.

Branhamella catarrhalis pneumonia: report of 4 cases.

This is the first time Branhamella Catarrhalis has been identified as a lower respiratory tract pathogen in Taiwan. All 4 patients with B. catarrhalis pneumonia reported herein had a certain degree of underlying pulmonary dysfunction. Two patients had pure B. catarrhalis infection, whilst the other two had concomitant infections with Haemophilus influenzae or Viridans streptococci. Amongst the 3 strains of B. catarrhalis examined, all were capable of producing beta-lactamase. By using the Kirby-Bauer method, 2 of these strains were observed as penicillin resistant. Therefore, patients with poor clinical response to penicillin, ampicillin, and cephapirin were treated effectively with trimethoprim/sulfamethoxazole or ofloxacin. B. catarrhalis should no longer be regarded as a normal flora of the sputum in patients with lower respiratory tract infections. Beta-lactamase production should be tested for each isolated strain to avoid failure of penicillin therapy due to bacterial resistance.

Clostridium perfringens septicemia with massive hemolysis.

Massive hemolysis with acute renal failure occurred in a previously healthy 69-year-old patient as a complication of Clostridium perfringens septicemia secondary to gall bladder empyema. To our knowledge, this is one of the few patients with C. perfringens septicemia and massive intravascular hemolysis who survived the episode and regained a normal renal function.