As only the type II topoisomerase is capable of introducing negative supercoiling, DNA gyrase is involved in crucial cellular processes. Although the other domains of DNA gyrase are better understood, the mechanism of DNA binding by the C-terminal domain of the DNA gyrase A subunit (GyrA-CTD) is less clear. Here, we investigated the DNA-binding sites in the GyrA-CTD of Mycobacterium tuberculosis gyrase through site-directed mutagenesis. The results show that Y577, R691 and R745 are among the key DNA-binding residues in M.tuberculosis GyrA-CTD, and that the third blade of the GyrA-CTD is the main DNA-binding region in M.tuberculosis DNA gyrase. The substitutions of Y577A, D669A, R691A, R745A and G729W led to the loss of supercoiling and relaxation activities, although they had a little effect on the drug-dependent DNA cleavage and decatenation activities, and had no effect on the ATPase activity. Taken together, these results showed that the GyrA-CTD is essential to DNA gyrase of M.tuberculosis, and promote the idea that the M.tuberculosis GyrA-CTD is a new potential target for drug design. It is the first time that the DNA-binding sites in GyrA-CTD have been identified.

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The recent novel severe acute respiratory syndrome coronavirus 2 infection resulted in a coronavirus disease 2019 pandemic that significantly strained healthcare systems globally. The early wave of patients in Singapore with severe pneumonia requiring intensive care units are gradually being referred for post–critical illness management with our inpatient medical rehabilitation unit. There is growing information regarding the actual rehabilitation process for patients severely affected by coronavirus disease 2019. This case report shares experiences and challenges faced during rehabilitation of severe coronavirus disease 2019 pneumonia and post–intensive care syndrome. It also describes the post–discharge rehabilitation program in a setting of strict nationwide safe distancing and stay-home policies.