functional studies of TB mmpl protein homologous

What is it about?

Corynebacterium–Mycobacterium–Nocardia (CMN) group are the causative agents of a broad spectrum of diseases in humans. A distinctive feature of these Gram-positive bacteria is the presence of an outer membrane of unique structure and composition. Recently, resistance–nodulation–division (RND) transporters (nicknamed MmpLs, Mycobacterial membrane protein Large) have emerged as major contributors to the biogenesis of the outer membranes in mycobacteria and as promising drug targets. In this study, we investigated the role of RND transporters in the physiology of Corynebacterium glutamicum and analyzed properties of these proteins. Our results show that in contrast to Gram-negative species, in which RND transporters actively extrude antibiotics from cells, in C. glutamicum and relatives these transporters protect cells from antibiotics by playing essential roles in the biogenesis of the low-permeability barrier of the outer membrane. Conditional C. glutamicum mutants lacking RND proteins and with the controlled expression of either NCgl2769 (CmpL1) or NCgl0228 (CmpL4) are hypersusceptible to multiple antibiotics, have growth deficiencies in minimal medium and accumulate intracellularly trehalose monocorynomycolates, free corynomycolates, and the previously uncharacterized corynomycolate-containing lipid. Our results also suggest that similar to other RND transporters, Corynebacterial membrane proteins Large (CmpLs) functions are dependent on a proton-motive force.

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Why is it important?

The CMN group share a distinctive cell envelope composition, characterized by the presence of a waxy cell outer membrane, containing mycolic acids, conferring alcohol and acid-fast staining properties on these bacteria, which distinguish them from other bacteria. However, how the elaborate outer memrbnae of CMN species are assembled remains unknown. Recent study identified the RND transporters in M. tuberculosis as the major contributors to the biogenesis of the outer membranes in mycrobacteria and promising drug targets. In this study we investigate the role of RND transporters in C. glutamicum, which share high sequence identity with M. tuberculosis MmpLs. We revealed that CmpLs are required for the cell growth and protect cells from antibiotics by playing essential roles in the biogenesis of outer membrane layer. Most importantly, our results provided strong evidence that the functions of MmpLs and CmpLs are conserved among CMN species. One of the difficulties of research on M. tuberculosis is that a significant higher secure level of laboratory and equipment are required to protect lab personals. In contrast, C. glutamicum can be handled in regular research environment. Therefore, CmpLs could server as a prototype for the study of MmpLs and help for the development of new drugs and vaccines.