| Popis: |
Mycobacteria grow and divide differently compared to well-studied model bacteria. They insert new cell envelope at their poles instead of along their side walls; and, they lack obvious homologs of many well-conserved cell growth and division proteins. Furthermore, while mycobacteria share several similarities to Gram-positive bacteria, unlike these organisms they possess an outer membrane, which is abundant in long-chain fatty acids and several glycolipids and lipoglycans. A better understanding of the unique factors that make this unusual structure could lead to therapeutic targets for pathogenic mycobacteria. Here, we study a gene of previously unknown function – msmeg_0317 - predicted to be essential and associated with mycobacterial cell growth and division proteins. We find that transcriptional depletion of msmeg_0317 leads to loss of polar growth, disruption of the mycobacterial outer membrane, and cell death. Surprisingly, we also observe that depletion results in the accumulation of cell-associated lipoglycans lipomannan and lipoarabinomannan (LM/LAM), while overexpression of CwdA leads to increased shedding of LM/LAM. LM/LAM have been extensively studied in relation to infection but their role in bacterial physiology is less clear. Altogether, our data suggest that MSMEG_0317, renamed CwdA, is involved in the transport of LM/LAM to the mycobacterial outer membrane, and reveal unexpected connections between the correct localization of LM/LAM, polar growth, and the structural integrity of the mycobacterial cell envelope. IMPORTANCE Some of the most successful antibiotics target bacterial cell envelope synthesis. However, the cell envelope of mycobacteria is significantly different from that of other, more well-studied, bacteria. Its core structure consists of a covalently-linked network of peptides, carbohydrates, and fatty acids. Additionally, there are several lipids non-covalently interspersed throughout. Many of the enzymes which synthesize these lipids are known, but how they are transported remains largely unclear. Here, we discover that an essential protein, CwdA, is involved in the transport of LM/LAM, abundant lipoglycans in the mycobacterial cell envelope. Depletion of CwdA leads to the loss of polar growth and the disintegration of the mycobacterial outer membrane. These results suggest that the proteins which transport molecules across the mycobacterial cell envelope may represent an abundant source of novel drug targets for the treatment of mycobacterial infections, like tuberculosis. |
