The extended N-terminus of Mycobacterium smegmatis RecX potentiates its ability to antagonize RecA functions

• Published in: Biochimica et biophysica acta. Proteins and proteomics 2020-10, Vol.1868 (10), p.140468, Article 140468
• Main Authors: Prasad, Deepika, Muniyappa, Kalappa
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Amino Acid Sequence; ATPase; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Conserved Sequence; DNA strand exchange; Evolution, Molecular; Genetic Variation; Genome stability; Hydrolysis; Mycobacterium Infections, Nontuberculous - microbiology; Mycobacterium smegmatis - physiology; Protein Binding; Protein Folding; Protein Interaction Domains and Motifs; Rec A Recombinases - antagonists & inhibitors; RecA nucleoprotein filaments; RecX anti-recombinase; Sequence Deletion; SOS response; Structure-Activity Relationship
• ISSN: 1570-9639; 1878-1454
• DOI: 10.1016/j.bbapap.2020.140468

The members of the RecX family of proteins have a unique capacity to regulate the catalytic activities of RecA/Rad51 proteins in both prokaryotic and eukaryotic organisms. However, our understanding of the functional roles of RecX in pathogenic and non-pathogenic mycobacteria has been limited by insufficient knowledge of the molecular mechanisms of its activity and regulation. Moreover, the significance of a unique 14 amino acid N-terminal extension in Mycobacterium smegmatis RecX (MsRecX) to its function remains unknown. Here, we advance our understanding of the antagonistic roles of mycobacterial RecX proteins and the functional significance of the extended N-terminus of MsRecX. The full-length MsRecX acts as an antagonist of RecA, negatively regulating RecA promoted functions, including DNA strand exchange, LexA cleavage and ATP hydrolysis, but not binding of ATP. The N-terminally truncated MsRecX variants retain the RecA inhibitory activity, albeit with lower efficiencies compared to the full-length protein. Perhaps most importantly, direct visualization of RecA nucleoprotein filaments, which had been incubated with RecX proteins, showed that they promote disassembly of nucleoprotein filaments primarily within the filaments. In addition, interaction of RecX proteins with the RecA nucleoprotein filaments results in the formation of stiff and irregularly shaped nucleoprotein filaments. Thus, these findings add an additional mechanism by which RecX disassembles RecA nucleoprotein filaments. Overall, this study provides strong evidence for the notion that the N-terminal 14 amino acid region of MsRecX plays an important role in the negative regulation of RecA functions and new insights into the molecular mechanism underlying RecX function. [Display omitted] •RecX is essential to counteract the toxic effects of RecA.•Little is known about RecX in pathogenic and non-pathogenic mycobacteria.•MsRecX has a unique N-terminal 14 amino acid region whose functional significance remains unknown.•The N-terminal 14 amino acid region of MsRecX is essential for its full inhibitory activity.•N-terminally truncated MsRecX variants retain the inhibitory activity, albeit at lower efficiency.