RESUMO
Nature utilizes three distinct pathways to synthesize the essential enzyme cofactor heme. The coproporphyrin III-dependent pathway, predominantly present in Bacillaceae, employs an oxygen-dependent coproporphyrinogen III oxidase (CgoX) that converts coproporphyrinogen III into coproporphyrin III. In this study, we report the bioinformatic-based identification of a gene called ytpQ, encoding a putative oxygen-independent counterpart, which we propose to term CgoN, from Priestia (Bacillus) megaterium. The recombinantly produced, purified, and monomeric YtpQ (CgoN) protein is shown to catalyze the oxygen-independent conversion of coproporphyrinogen III into coproporphyrin III. Minimal non-enzymatic conversion of coproporphyrinogen III was observed under the anaerobic test conditions employed in this study. FAD was identified as a cofactor, and menadione served as an artificial acceptor for the six abstracted electrons, with a KM value of 3.95 µmol/L and a kcat of 0.63 per min for the substrate. The resulting coproporphyrin III, in turn, acts as an effective substrate for the subsequent enzyme of the pathway, the coproporphyrin III ferrochelatase (CpfC). Under aerobic conditions, oxygen directly serves as an electron acceptor, but is replaced by the more efficient action of menadione. An AlphaFold2 model of the enzyme suggests that YtpQ adopts a compact triangular shape consisting of three domains. The N-terminal domain appears to be flexible with respect to the rest of the structure, potentially creating a ligand binding site that opens and closes during the catalytic cycle. A catalytic mechanism similar to the oxygen-independent protoporphyrinogen IX oxidase PgoH1 (HemG), based on the flavin-dependent abstraction of six electrons from coproporphyrinogen III and their potential quinone-dependent transfer to a membrane-localized electron transport chain, is proposed.
RESUMO
Background: At the beginning of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, transfusion of coronavirus disease 2019 (COVID-19) convalescent plasma (CCP) emerged as a potential therapeutic strategy to help patients severely afflicted by COVID-19. The efficacy of CCP has been controversial as it depends on many variables pertaining to the plasma donor and the patient with COVID-19, for example, time of convalescence or symptoms onset. This feasibility and descriptive study aimed to assess the safety of multiple doses of CCP in mechanically ventilated, intubated patients with respiratory failure due to COVID-19. Methods: A cohort of 30 patients all experiencing severe respiratory failure and undergoing invasive mechanical ventilation in an intensive care unit, received up to five doses of 300-600 mL of CCP on alternate days (0, 2, 4, 6, and 8) until extubation, futility, or death. Results: Nineteen patients received five doses, seven received four, and four received two or three doses. At 28-day follow-up mark, 57% of patients recovered and were sent home, and the long-term mortality rate was 27%. Ten severe adverse events reported in the study were unrelated to CCP transfusion. Independent of the number of transfused doses, most patients had detectable levels of total and neutralizing antibodies in plasma. Conclusion: This study suggests that transfusion of multiple doses of CCP is safe. This strategy may represent a viable option for future studies, given the potential benefit of CCP transfusions during the early stages of infection in unvaccinated populations and in settings where monoclonal antibodies or antivirals are contraindicated or unavailable.
