Peptidoglycan
PG is a thick, macromolecular mesh made up of long GlcNAc-MurNAc glycan strands crosslinked to one another by short oligopeptides. This mesh layer is crucial for bacterial cell survival, and PG biosynthesis is therefore an important target for antibiotics, both old and new.
wall teichoic acids
WTA polymers in S. aureus are made up mostly of ribitol phosphate monomers, and similarly to LTAs, they are important for governing cell size, division, and envelope integrity. Interestingly, methicillin-resistant strains of S. aureus become sensitized to beta-lactams when WTA biosynthesis is inhibited. Thus, targeting enzymes involved in this process is a possible strategy for MRSA infection treatment.
cell envelope overview
The cell envelope of Gram-positive bacteria consists of a thick peptidoglycan (PG, light blue) layer surrounding the membrane bilayer. Additionally, most Gram-positive species, including Staphylococcus aureus, have lipoteichoic acids (LTAs, yellow) embedded in the outer leaflet of the membrane and wall teichoic acids (WTAs, magenta) covalently linked to PG.
lipoteichoic acids
In S. aureus, LTA polymers are composed of glycerol phosphate monomers, and their presence is essential for cell viability in many strains. LTAs are crucial for bacterial virulence, and they are also important for controlling cell size, cell division, and cell envelope integrity. Because of these important roles, LTA biosynthesis is a potential antibiotic target.
Our longterm goal is to understand how the bacterial cell envelope is assembled, how its assembly is coordinated with cell division, and how we can exploit our knowledge to develop strategies to overcome antibiotic-resistant infections. Our primary model system is Staphylococcus aureus. We have developed a wide range of tools and methods to study peptidoglycan biosynthesis and degradation. We have reconstituted lipo- and wall teichoic acid biosynthesis pathways. We have developed new approaches to discover inhibitors of biosynthetic enzymes in these pathways, and we have established genome-wide approaches that use small molecules to uncover connections between pathways. We now want to combine our tools and approaches with other technologies to develop an integrated picture of how extracellular and intracellular biosynthesis pathways are coordinated through the cell membrane to allow the cell to grow and divide.
To read more about some of our work on the bacterial cell envelope, please see the selected publications below.
selected publications
Hesser, A. R.; Schaefer, K.; Lee, W.; Walker, S. Lipoteichoic acid polymer length is determined by competition between free starter units. Proc. Natl. Acad. Sci. U. S. A. 2020, 117 (47), 29669-29676. [PubMed Link] [Publisher Link]
#Schaefer, K.; #Owens, T. W.; Page, J. E.; Santiago, M.; Kahne, D.; Walker, S. Structure and reconstitution of a hydrolase complex that may release peptidoglycan from the membrane after polymerization. Nat. Microbiol. 2020, 6, 34-43. [PubMed Link] [Publisher Link]
Do, T.; Schaefer, K.; Santiago, A. G.; Coe, K. A.; Fernandes, P. B.; Kahne, D.; Pinho, M. G.; Walker, S. Staphylococcus aureus cell growth and division are regulated by an amidase that trims peptides from uncrosslinked peptidoglycan. Nat. Microbiol. 2020, 5 (2), 291-303. [PubMed Link] [Publisher Link]
Taguchi, A.; Welsh, M. A.; Marmont, L. S.; Lee, W.; Sjodt, M.; Kruse, A. C.; Kahne, D.; Bernhardt, T. G.; Walker, S. FtsW is a peptidoglycan polymerase that is functional only in complex with its cognate penicillin-binding protein. Nat. Microbiol. 2019, 4, 587-594. [PubMed Link] [Publisher Link]
Santiago, M.; Lee, W.; Fayad, A. A.; Coe, K. A.; Rajagopal, M.; Do, T.; Hennessen, F.; Srisuknimit, V.; Müller, R.; Meredith, T. C.; Walker, S. Genome-wide mutant profiling predicts the mechanism of a Lipid II binding antibiotic. Nat. Chem. Biol. 2018, 14 (6), 601-608. [PubMed Link] [Publisher Link]
Schaefer, K.; Owens, T. W.; Kahne, D.; Walker, S. Substrate Preferences Establish the Order of Cell Wall Assembly in Staphylococcus aureus. J. Am. Chem. Soc. 2018, 140 (7), 2442-2445. [PubMed Link] [Publisher Link]
Schaefer, K.; Matano, L. M.; Qiao, Y.; Kahne, D.; Walker, S. In vitro reconstitution demonstrates the cell wall ligase activity of LCP proteins. Nat. Chem. Biol. 2017, 13 (4), 396-401. [PubMed Link] [Publisher Link]
Pasquina, L.; Santa Maria, J. P.; Wood, B. M.; Moussa, S. H.; Matano, L. M.; Santiago, M.; Martin, S. E. S.; Lee, W.; Meredith, T. C.; Walker, S. A synthetic lethal approach for compound and target identification in Staphylococcus aureus. Nat. Chem. Biol. 2016, 12 (1), 40-45. [PubMed Link] [Publisher Link]
Qiao, Y.; Lebar, M. D.; Schirner, K.; Schaefer, K.; Tsukamoto, H.; Kahne, D.; Walker, S. Detection of Lipid-Linked Peptidoglycan Precursors by Exploiting an Unexpected Transpeptidase Reaction. J. Am. Chem. Soc. 2014, 136 (42), 14678-14681. [PubMed Link] [Publisher Link]
Santa Maria, J. P.; Sadaka, A.; Moussa, S. H.; Brown, S.; Zhang, Y. J.; Rubin, E. J.; Gilmore, M. S.; Walker, S. Compound-gene interaction mapping reveals distinct roles for Staphylococcus aureus teichoic acids. Proc. Natl. Acad. Sci. U. S. A. 2014, 111 (34), 12510-12515. [PubMed Link] [Publisher Link]
Brown, S.; Xia, G.; Luhachack, L. G.; Campbell, J.; Meredith, T. C.; Chen, C.; Winstel, V.; Gekeler, C.; Irazoqui, J. E.; Peschel, A.; Walker, S. Methicillin resistance in Staphylococcus aureus requires glycosylated wall teichoic acids. Proc. Natl. Acad. Sci. U. S. A. 2012, 109 (46), 18909-18914. [PubMed Link] [Publisher Link]
Campbell, J.; Singh, A. K.; Santa Maria, J. P.; Kim, Y.; Brown, S.; Swoboda, J. G.; Mylonakis, E.; Wilkinson, B. J.; Walker, S. Synthetic Lethal Compound Combinations Reveal a Fundamental Connection between Wall Teichoic Acid and Peptidoglycan Biosynthesis in Staphylococcus aureus. ACS Chem. Biol. 2011, 6 (1), 106-116. [PubMed Link] [Publisher Link]