Role of conserved F(alpha)-helix residues in the native fold and stability of the kinase-inhibited oxy state of the oxygen-sensing FixL protein from Sinorhizobium meliloti.

The oxygen-sensing FixL protein from Sinorhizobium meliloti is part of the heme-PAS family of gas sensors that regulate many important signal transduction pathways in a wide variety of organisms. We examined the role of the conserved F(alpha)-9 arginine 200 and several other conserved residues on the proximal F(alpha)-helix in the heme domain of SmFixL* using site-directed mutagenesis in conjunction with UV-visible, EPR, and resonance Raman spectroscopy. The F(alpha)-helix variants R200A, E, Q, H, Y197A, and D195A were expressed at reasonable levels and purified to homogeneity. The R200I and Y201A variants did not express in observable quantities. Tyrosine 201 is crucial for forming the native protein fold of SmFixL* while Y197 and R200 are important for stabilizing the kinase-inhibited oxy state. Our results show a clear correlation between H-bond donor ability of the F(alpha)-9 side chain and the rate of heme autoxidation. This trend in conjunction with crystal structures of liganded BjFixL heme domains, show that H-bonding between the conserved F(alpha)-9 arginine and the heme-6-propionate group contributes to the kinetic stability of the kinase-inactivated, oxy state of SmFixL*.

A 22-year-old man with pleural tuberculosis associated hydropneumothorax: Case report and literature review.

A 22-year-old Asian male presented with fever, non-productive cough, right-sided pleuritic chest pain and was found to have a large right hydropneumothorax. A chest tube was placed. Pleural fluid analysis revealed a lymphocytic predominant exudate and he was subsequently started on four-drug daily anti-tuberculosis therapy (isoniazid, ethambutol, rifampin, pyrazinamide). Pleural biopsy revealed acid-fast bacilli. Given his persistent pleural effusion, he was given four doses of intrapleural tissue plasminogen activator (tPA) and dornase alpha (DNase) via his chest tube over a period of 6 days resulting in clinical and radiologic improvement. Pleural biopsy and pleural fluid culture specimens later revealed Mycobacterium tuberculosis. Intrapleural tPA-DNase therapy has demonstrated improved resolution of infections and shortened hospitalizations for parapneumonic infectious effusions. However, there is little literature on the use of intrapleural fibrinolytics specifically for pleural tuberculosis associated effusions. Furthermore, the American Thoracic Society does not comment on therapeutic thoracentesis or intrapleural fibrinolytic therapy in their recommendations for treatment of pleural tuberculosis. In our case of pleural TB-associated hydropneumothorax, the use of intrapleural tPA-DNase therapy facilitated pleural fluid drainage and resulted in near-complete resolution of the effusion.