NEWS Bacteria are small but tough organisms, partly because their cells are enclosed by a protective cell wall skeleton. Professor Felipe Cava and his team at Umeå University in Sweden and collaborators at Harvard Medical School in the USA, have discovered long-sought proteins needed to maintain the bacterial cell wall structure. These proteins represent a very promising vulnerability for many bacteria that can be exploited by future antimicrobial compounds. The findings are published in Nature.
Professor Felipe Cava and postdoctor fellow Emilio Bueno, Department of Molecular Biology, have made their discoveries together with researchers at the Harvard Medicical School in the USA.
ImageMattias PetterssonInterestingly, some of these proteins are only required under specific conditions
“We found that two poorly characterized protein families, DUF368 and DedA, which are widely conserved in all three major groups of life, are responsible for the recycling of the lipid carriers. Interestingly, some of these proteins are only required under specific conditions, which suggests that the transport function is dynamic and regulated by different environmental signals,” says Felipe Cava, professor at the Department of Molecular Biology at Umeå University.
Using the model organisms Vibrio cholerae and Staphylococcus aureus, the team of infection researchers associated with the Laboratory for Molecular Infection Medicine Sweden (MIMS) and the Umeå Center for Microbial Research (UCMR) at Umeå University in collaboration with researchers from Harvard Medical School in the USA made their discovery that now is published in the prestigious journal Nature.
Recycling of lipid carriers is critical to the ability of pathogenic bacteria to initiate disease, suggesting that selectively targeting these transporters could be a viable and significant approach to developing new antimicrobial agents.
Proteins are found in screening
The cell wall, like the skin of animals, is essential for bacteria to stay alive. Many of our best antibiotics therefore target the proteins that build and remodel this structure. As the cell wall is located on the outside of the cell membrane that encloses the cell, its building blocks must be transported across this membrane from where they are made, the cytoplasm. To carry out this transfer, bacteria use a specialized lipid carrier called undecaprenyl phosphate.
Once these building blocks are delivered and assembled the lipid carrier must return to the cytoplasm to transport new units; however, the identity of the proteins recycling these lipids remained elusive until now.
Schematic representation of cell wall synthesis in bacteria.
ImageIllustration by Emilio BuenoMotivated by an in vivo screening of gut colonization factors for V. cholerae, the research team was able to identify a membrane protein that contained the widely conserved domain, DUF368. The experiments showed that in the absence of DUF368-containing proteins, both model bacteria grew poorly and exhibited morphological defects strongly suggesting that these membrane proteins are involved in cell wall biogenesis, and especially in the transport of undecaprenyl phosphate lipids.
Selection of transport protein is dynamic
Since lipid carrier recycling is such an important function, it was notable that DUF368 mutants were mostly affected at alkaline pH. This suggests that there are other transporters at neutral and acidic pH values in the cell. A screen identified a protein of the DedA family as an additional transporter of undecaprenyl phosphate. The results show that the context controls the activity around the recycling of undecaprenyl phosphate in bacterial cells.
“Bacteria normally experience a wide range of environmental changes both under free-living conditions and during infection. The choice of specific undecaprenyl phosphate transport proteins to maintain cell wall stability in the various situations appears to be an adaptive mechanism in bacteria,” explains Emilio Bueno, postdoctoral fellow at the Department of Molecular Biology at Umeå University.
Professor Felipe Cava and postdoctor fellow Emilio Bueno in their research laboratory.
ImageMattias PetterssonIdeal target for antibiotics
Recycling of undecaprenyl phosphate is a key step in the biosynthesis of not only peptidoglycan, the primary structural component of the cell wall, but also other cell surface glycopolymers, including wall teichoic acid, some lipopolysaccharide modifications, and capsules.
“Given its extensive and critical role in the maintenance of bacterial cell surfaces, this step is an ideal target for antimicrobial agents. Furthermore, although DUF368 proteins are restricted to bacteria and archaea, DedA family members are ubiquitous in eukaryotes, including humans. Therefore, our findings can influence the understanding of polyprenyl phosphate transport in all three major groups of life," says Felipe Cava.
Brandon Sit, Veerasak Srisuknimit, Emilio Bueno, Franz G. Zingl, Karthik Hullahalli, Felipe Cava, Matthew K. Waldor (2022): Undecaprenyl phosphate translocases confer conditional microbial fitness. Nature (2022). https://doi.org/10.1038/s41586-022-05569-1
