Bacterial cell walls are formidable barriers that protect bacterial cells against external insults and oppose internal turgor pressure. While cell wall composition is variable across species, peptidoglycan is the principal component of all cell walls. Peptidoglycan is a mesh-like scaffold composed of cross-linked strands that can be heavily decorated with anchored proteins. The biosynthesis and remodeling of peptidoglycan must be tightly regulated by cells because disruption to this biomacromolecule is lethal. This essentiality is exploited by the human innate immune system in resisting colonization and by a number of clinically relevant antibiotics that target peptidoglycan biosynthesis. Evaluation of molecules or proteins that interact with peptidoglycan can be a complicated and, typically, qualitative effort. We have developed a novel assay platform (SaccuFlow) that preserves the native structure of bacterial peptidoglycan and is compatible with high-throughput flow cytometry analysis. We show that the assay is facile and versatile as demonstrated by its compatibility with sacculi from Gram-positive bacteria, Gram-negative bacteria, and mycobacteria. Finally, we highlight the utility of this assay to assess the activity of sortase A from Staphylococcus aureus against potential antivirulence agents.
Proteins from bacterial foes, antimicrobial peptides, and host immune proteins must navigate past a dense layer of bacterial surface biomacromolecules to reach the peptidoglycan (PG) layer of Gram-positive bacteria. A subclass of molecules (e.g., antibiotics with intracellular targets) also must permeate through the PG (in a molecular sieving manner) to reach the cytoplasmic membrane. Despite the biological and therapeutic importance of surface accessibility, systematic analyses in live bacterial cells have been lacking. We describe a live cell fluorescence assay that is robust, shows a high level of reproducibility, and reports on the permeability of molecules to and within the PG scaffold. Moreover, our study shows that teichoic acids impede the permeability of molecules of a wide range of sizes and chemical composition.
A growing class of immunotherapeutic agents work by redirecting components of the immune system to recognize specific markers on the surface of cancer cells and initiate a selective immune response. However, such immunotherapeutic modalities will remain confined to a relatively small subgroup of patients until two major hurdles are overcome: (1) the specific targeting of cancer cells relative to healthy cells, and (2) the lack of common targetable tumor biomarkers among all patients. Here, we designed a unique class of agents that exploit the inherent acidic microenvironment of solid tumors to selectively graft the surface of cancer cells with immuno-engager epitopes for directed destruction by components of the immune system. Specifically, conjugates were assembled using an antigen that recruit antibodies present in human serum, and the pH(Low) Insertion Peptide (pHLIP), a unique peptide that selectively target tumors in vivo by anchoring onto cancer cell surfaces in a pHdependent manner. We established that conjugates can recruit antibodies from human serum to the surface of cancer cells, and induce complementdependent and antibody-dependent cellular cytotoxicity by peripheral blood mononuclear cells and also an engineered NK cell line. These results suggest that these agents have the potential to be applicable to treating a wide range of solid tumors and to circumvent the problem of narrow windows of selectivity..
Bacterial cell walls are formidable barriers that protect bacterial cells against external insults and oppose internal turgor pressure. While cell wall composition is variable across species, peptidoglycan is the principal component of all cell walls. Peptidoglycan is a mesh-like scaffold composed of crosslinked strands that can be heavily decorated with anchored proteins. The biosynthesis and remodeling of peptidoglycan must be tightly regulated by cells because disruption to this biomacromolecule is lethal. This essentiality is exploited by the human innate immune system in resisting colonization and by a number of clinically relevant antibiotics that target peptidoglycan biosynthesis. Evaluation of molecules or proteins that interact with peptidoglycan can be a complicated and, typically, qualitative effort. We have developed a novel assay platform (SaccuFlow) that preserves the native structure of bacterial peptidoglycan and is compatible with high-throughput flow cytometry analysis. We show that the assay is facile and versatile as demonstrated by its compatibility with sacculi from Gram-positive bacteria, Gram-negative bacteria, and mycobacteria. Finally, we highlight the utility of this assay to assess the activity of sortase from Staphylococcus aureus against potential anti-virulence agents.
A growing class of immunotherapeutic agents work by redirecting components of the immune system to recognize specific markers on the surface of cancer cells and initiate a selective immune response. However, such immunotherapeutic modalities will remain confined to a relatively small subgroup of patients until two major hurdles are overcome: (1) the specific targeting of cancer cells relative to healthy cells, and (2) the lack of common targetable tumor biomarkers among all patients. Here, we designed a unique class of agents that exploit the inherent acidic microenvironment of solid tumors to selectively graft the surface of cancer cells with immuno-engager epitopes for directed destruction by components of the immune system. Specifically, conjugates were assembled using an antigen that recruit antibodies present in human serum, and the pH(Low) Insertion Peptide (pHLIP), a unique peptide that selectively target tumors in vivo by anchoring onto cancer cell surfaces in a pHdependent manner. We established that conjugates can recruit antibodies from human serum to the surface of cancer cells, and induce complementdependent and antibody-dependent cellular cytotoxicity by peripheral blood mononuclear cells and also an engineered NK cell line. These results suggest that these agents have the potential to be applicable to treating a wide range of solid tumors and to circumvent the problem of narrow windows of selectivity.
Bacterial cell walls represent one of the most prominent targets of antibacterial agents. These agents include natural products (e.g., vancomycin) and proteins stemming from the innate immune system (e.g., peptidoglycan-recognition proteins and lysostaphin). Among bacterial pathogens that infect humans, Staphylococcus aureus (S. aureus) continues to impose a tremendous healthcare burden across the globe. S. aureus has evolved countermeasures that can directly restrict the accessibility of innate immune proteins, effectively protecting itself from threats that target key cell well components. We recently described a novel assay that directly reports on the accessibility of molecules to the peptidoglycan layer within the bacterial cell wall of S. aureus. The assay relies on site-specific chemical remodeling of the peptidoglycan with a biorthogonal handle. Here, we disclose the application of our assay to a screen of a nonredundant transposon mutant library for susceptibility of the peptidoglycan layer with the goal of identifying genes that contribute to the control of cell surface accessibility. We discovered several genes that resulted in higher accessibility levels to the peptidoglycan layer and showed that these genes modulate sensitivity to lysostaphin. These results indicate that this assay platform can be leveraged to gain further insight into the biology of bacterial cell surfaces.
Current immunotherapeutics often work by directing components of the immune system to recognize biomarkers on the surface of cancer cells to generate an immune response. However, variable changes in biomarker distribution and expression can result in inconsistent patient response. The development of a more universal tumor‐homing strategy has the potential to improve selectivity and extend therapy to cancers with decreased expression or absence of specific biomarkers. Here, we designed a bifunctional agent that exploits the inherent acidic microenvironment of most solid tumors to selectively graft the surface of cancer cells with a formyl peptide receptor ligand (FPRL). Our approach is based on the pH(Low) insertion peptide (pHLIP), a unique peptide that selectively targets tumors in vivo by anchoring to cancer cells in a pH‐dependent manner. We establish that selectively remodeling cancer cells with a pHLIP‐based FPRL activates formyl peptide receptors on recruited immune cells, potentially initiating an immune response towards tumors.
Bacterial cell walls represent one of the most prominent targets of antibacterial agents. These agents include natural products (e.g., vancomycin) and proteins stemming from the innate immune system (e.g., peptidoglycan-recognition proteins and lysostaphin). Among bacterial pathogens that infect humans, Staphylococcus aureus (S. aureus) continues to impose a tremendous healthcare burden across the globe. S. aureus has evolved countermeasures that can directly restrict the accessibility of innate immune proteins, effectively protecting itself from threats that target key cell well components. We recently described a novel assay that directly reports on the accessibility of molecules to the peptidoglycan layer within the bacterial cell wall of S. aureus. The assay relies on site-specific chemical remodeling of the peptidoglycan with a biorthogonal handle. Here, we disclose the application of our assay to a screen of a nonredundant transposon mutant library for susceptibility of the peptidoglycan layer with the goal of identifying genes that contribute to the control of cell surface accessibility. We discovered several genes that resulted in higher accessibility levels to the peptidoglycan layer and showed that these genes modulate sensitivity to lysostaphin. These results indicate that this assay platform can be leveraged to gain further insight into the biology of bacterial cell surfaces.
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