A bacterial protein ties cell wall lipids to envelope strength

Tuberculosis, caused by Mycobacterium tuberculosis (Mtb), remains a major global health challenge, and scientists are searching for new ways to weaken the bacterium’s protective outer layers. One promising target is Rv0647c, an essential Mtb cell wall protein. In the study led by corresponding author Boris Tefsen, researchers turned to Mycolicibacterium smegmatis, a nonpathogenic relative, to investigate the function of the equivalent gene, MSMEG_1353. Using a CRISPRi conditional knockdown approach, the team reduced MSMEG_1353 levels to observe how the bacteria responded. The goal was to link this gene to the processes that build and maintain the complex lipid-rich envelope that shields mycobacteria, a structure that is central to their survival and to how they resist antibiotics. By combining genetic knockdown with structural prediction and biochemical measurements, the researchers aimed to map how MSMEG_1353 influences both the physical shape of the cell and the metabolic pathways that create mycolic acids and other envelope lipids.

The researchers used a suite of tools to probe MSMEG_1353 function. CRISPRi-mediated depletion of MSMEG_1353 produced clear physical and physiological changes: cells became wider and larger in volume, entry into log-phase growth was delayed, cell aggregation slowed, biofilm formation decreased, and bacteria became more susceptible to antibiotics and sodium dodecyl sulfate (SDS). To explore protein function, the team applied AlphaFold structural predictions, sequence alignment, and UNIPROT database analysis; these lines of evidence suggest MSMEG_1353 acts as a protein kinase, with conserved residues in intermediate high-confidence regions that could form an ATP-binding site. Mass spectrometry showed elevated levels of mycolic acid biosynthesis proteins when MSMEG_1353 was knocked down, and RT-qPCR confirmed upregulation of the fabD-acpM-kasA-KasB-accD6 operon, which encodes key mycolic acid synthesis enzymes. Both mass spectrometry and RT-qPCR also revealed a strong negative correlation between MSMEG_1353 and MSMEG_0911, the predominant isocitrate lyase important in the glyoxylate cycle.

Taken together, these findings indicate that loss of MSMEG_1353 compromises cell wall integrity, likely by changing the balance of lipid production and metabolism that constructs the mycobacterial envelope. Dysregulated mycolic acid biosynthesis and altered connections to central metabolism — exemplified by the inverse relationship with MSMEG_0911 — point to a broader role for MSMEG_1353 in coordinating lipid pathways with envelope assembly. If MSMEG_1353 indeed functions as a kinase that helps regulate these processes, it could explain why its depletion makes cells more vulnerable to detergents like SDS and to antibiotics: the protective lipid barrier is weakened. These results provide a basis for developing models of how MSMEG_1353 links enzymatic control, lipid synthesis, and envelope structure, and they strengthen the rationale for studying the Mtb homologue Rv0647c as a potential drug target that might sensitize mycobacteria to existing treatments.