Publication Highlight
A potential target for myobacteria
This publication highlight is part of the SBGrid/Meharry Medical College Communities Project, focused on science education and demonstrating how structural biology and preclinical science connect to medicine.
Mycobacteria are a group of bacteria that include the pathogen Mycobacterium tuberculosis, the causative agent of tuberculosis. These bacteria are characterized by their thick, waxy cell walls, which make them highly resistant to antibiotics, environmental stress, and host immune defenses. To survive harsh conditions, mycobacteria rely on DNA repair mechanisms that ensure genome stability. One of these mechanisms is controlled by the transcription factor PafBC, which regulates genes involved in the bacterial DNA damage response. While the traditional bacterial DNA repair response is well understood, the exact mechanism by which PafBC is activated remained unclear. A new study by SBGrid member Eilika Weber-Ban from ETH Zurich, and colleagues, reveals that PafBC is directly activated by single-stranded DNA (ssDNA), providing new insights into bacterial stress responses and potential antibiotic targets.
In their work titled “Single-stranded DNA binding to the transcription factor PafBC triggers the mycobacterial DNA damage response,” these researchers found that ssDNA, a product of damaged DNA, binds directly to the WYL domains of PafBC. (The WYL domains are a group of proteins that regulate gene expression by binding to DNA or RNA) . PafBC binding to ssDNA triggers its activation. Using cryo-electron microscopy, they captured PafBC in its active state and discovered a previously unknown ssDNA-binding tunnel spanning the WYL and WCX domains. This finding suggests that ssDNA acts as a signal for PafBC activation, linking DNA damage directly to the bacterial transcriptional response. Unlike other transcription factors that require additional proteins for activation, PafBC is regulated by the presence of ssDNA alone. This difference suggests that mycobacteria have evolved a unique strategy for DNA repair, allowing them to respond rapidly to stress conditions.
Further experiments revealed that PafBC does not function independently but requires RNA polymerase to be pre-bound to DNA before forming a stable complex. RNA polymerase, an enzyme responsible for transcribing DNA into RNA, first attaches to a specific promoter sequence on the bacterial genome. Once ssDNA binds PafBC, it facilitates the recruitment of RNA polymerase, enabling the transcription of DNA repair genes. The study also showed that PafBC activation is dynamic and reversible. As DNA repair is completed and ssDNA levels decrease, PafBC is deactivated, halting the transcription of repair genes. This regulatory mechanism prevents excessive gene expression and allows the bacterium to adapt to changing conditions. Biochemical analyses also demonstrated that ssDNA fragments as short as six nucleotides can activate PafBC, although longer sequences are more effective.
The findings of this study have significant implications for tuberculosis treatment and antibiotic development. By targeting PafBC or its ssDNA-binding mechanism, researchers may be able to develop new drugs that disrupt bacterial DNA repair, making bacteria more vulnerable to existing antibiotics. As antibiotic resistance continues to rise, understanding bacterial stress responses at the molecular level is crucial for designing more effective therapeutic strategies.
Read more in Science Advances.
By KeAndreya Morrison, Meharry Medical College
KeAndreya Morrison is a biomedical sciences Ph.D. Candidate at Meharry Medical College studying the relationship between host and pathogen through the lens of structural biology. KeAndreya is a Georgia native where she completed her bachelor’s degree in biology at Fort Valley State University in Fort Valley, GA.
