Domain swapping of the C-terminal helix promotes the dimerization of a novel ribonuclease protein from Mycobacterium tuberculosis

Polyketide metabolism-associated proteins in Mycobacterium tuberculosis play an essential role in the survival of the bacterium, which makes them potential drug targets for the treatment of tuberculosis (TB). The novel ribonuclease protein Rv1546 is predicted to be a member of the steroidogenic acute regulatory protein-related lipid-transfer (START) domain superfamily, which comprises bacterial polyketide aromatase/cyclases (ARO/CYCs). Here, we determined the crystal structure of Rv1546 in a V-shaped dimer. The Rv1546 monomer consists of four alpha-helices and seven antiparallel beta-strands. Interestingly, in the dimeric state, Rv1546 forms a helix-grip fold, which is present in START domain proteins, via three-dimensional domain swapping. Structural analysis revealed that the conformational change of the C-terminal alpha-helix of Rv1546 might contribute to the unique dimer structure. Site-directed mutagenesis followed by in vitro ribonuclease activity assays was performed to identify catalytic sites of the protein. This experiment suggested that surface residues R63, K84, K88, and R113 are important in the ribonuclease function of Rv1546. In summary, this study presents the structural and functional characterization of Rv1546 and supplies new perspectives for exploiting Rv1546 as a novel drug target for TB treatment.

Automated summary

Polyketide metabolism-associated proteins in Mycobacterium tuberculosis are crucial for the survival of the bacterium, making them potential drug targets for tuberculosis treatment. This study focuses on the structural and functional characterization of a novel ribonuclease protein, Rv1546, which belongs to the steroidogenic acute regulatory protein-related lipid-transfer (START) domain superfamily. The crystal structure of Rv1546 in a V-shaped dimer is determined, and it forms a helix-grip fold through three-dimensional domain swapping. Site-directed mutagenesis and ribonuclease activity assays identify important catalytic sites of Rv1546. Overall, these findings provide new insights into the potential of Rv1546 as a drug target for tuberculosis treatment.