The acidic C-terminal tail of DNA Gyrase of Salmonella enterica serovar Typhi controls DNA relaxation in an acidic environment

The intracellular bacteria, Salmonella Typhi adapts to acidic conditions in the host cell by resetting the chromosomal DNA topology majorly controlled by DNA Gyrase, a Type II topoisomerase. DNA Gyrase forms a heterodimer A2B2 complex, which manages the DNA supercoiling and relaxation in the cell. DNA relaxation forms a part of the regulatory mechanism to activate the transcription of genes required to survive under hostile conditions. Acid -induced stress attenuates the supercoiling activity of the DNA Gyrase, resulting in DNA relaxation. Salmonella DNA becomes relaxed as the bacteria adapt to the acidified intracellular environment. Despite comprehensive studies on DNA Gyrase, the mechanism to control supercoiling activity needs to be better understood. A loss in supercoiling activity in E. coli was observed upon deletion of the non -conserved acidic C -tail of Gyrase A subunit. Salmonella Gyrase also contains an acidic tail at the C -terminus of Gyrase A, where its deletion resulted in reduced supercoiling activity compared to wild -type Gyrase. Interestingly, we also found that wildtype Gyrase compromises supercoiling activity at acidic pH 2-3, thereby causing DNA relaxation. The absence of a C -tail displayed DNA supercoiling to some extent between pH 2-9. Hence, the C -tail of Gyrase A might be one of the controlling factors that cause DNA relaxation in Salmonella at acidic pH conditions. We propose that the presence of the C -tail of GyraseA causes acid -mediated inhibition of the negative supercoiling activity of Gyrase, resulting in relaxed DNA that attracts DNA -binding proteins for controlling the transcriptional response.