Newly discovered Staphylococcus aureus serine hydrolase probe and drug targets

Similar but Distinct-Biochemical Characterization of the Staphylococcus aureus Serine Hydrolases FphH and FphI

Staphylococcus aureus is a major cause of infections like bacteremia, pneumonia, and endocarditis. These infections are often linked to the ability of S. aureus to form biofilms. Several S. aureus serine hydrolases have previously been identified to be active during biofilm-forming conditions. Here, we present the biochemical characterization of two of these enzymes-fluorophosphonate binding hydrolase H and I (FphH, FphI). Cryogenic and room-temperature X-ray crystallography, enzymatic substrate profiling, small-angle X-ray scattering analysis, and molecular dynamics simulations provide new insights into similarities and differences between these two hydrolase_4 domain family members. We discover that these enzymes share an overall fold, including a flexible lid or cap region above the active site, which can be seen to be mobile in solution. Differences in the active site pocket and lid residues differentiate them and explain speed differences in their carboxyesterase substrate profile toward small unbranched carbon chain ester molecules. The first analysis of FphI is also compared to our previous knowledge of FphH and its association to stress conditions. These results enable the future precise targeting of Fph serine hydrolase family members with a long-term goal to significantly improve the health and wellbeing of individuals and populations worldwide.

Bioinformatics Analysis Suggests That SE_1780 Protein From Staphylococcus Epidermidis May Be a Member of the Fph Family of Lipases

The Protein Data Bank entry for protein SE_1780 from Staphylococcus epidermidis lists the function as unknown. We leveraged the framework outlined in the Biochemistry Authentic Scientific Inquiry Laboratory and used bioinformatics tools to ascertain the function of the protein. Based on our analysis, we posit that SE_1780 is a lipase of the α/β hydrolase family with a proposed active site catalytic triad composed of Ser 144, Asp 235, and His 269. Further we identified the lipase FphD as having significant sequence identity to protein SE_1780 and suggest that the protein is a member of the Fph family of lipases from S. epidermidis .

Development of Oxadiazolone Activity-Based Probes Targeting FphE for Specific Detection of Staphylococcus aureus Infections

Staphylococcus aureus (S. aureus) is a major human pathogen that is responsible for a wide range of systemic infections. Since its propensity to form biofilms in vivo poses formidable challenges for both detection and treatment, tools that can be used to specifically image S. aureus biofilms are highly valuable for clinical management. Here, we describe the development of oxadiazolone-based activity-based probes to target the S. aureus-specific serine hydrolase FphE. Because this enzyme lacks homologues in other bacteria, it is an ideal target for selective imaging of S. aureus infections. Using X-ray crystallography, direct cell labeling, and mouse models of infection, we demonstrate that oxadiazolone-based probes enable specific labeling of S. aureus bacteria through the direct covalent modification of the FphE active site serine. These results demonstrate the utility of the oxadizolone electrophile for activity-based probes and validate FphE as a target for the development of imaging contrast agents for the rapid detection of S. aureus infections.

Biochemical and Cellular Characterization of the Function of Fluorophosphonate-Binding Hydrolase H (FphH) in Staphylococcus aureus Support a Role in Bacterial Stress Response

The development of new treatment options for bacterial infections requires access to new targets for antibiotics and antivirulence strategies. Chemoproteomic approaches are powerful tools for profiling and identifying novel druggable target candidates, but their functions often remain uncharacterized. Previously, we used activity-based protein profiling in the opportunistic pathogen Staphylococcus aureus to identify active serine hydrolases termed fluorophosphonate-binding hydrolases (Fph). Here, we provide the first characterization of S. aureus FphH, a conserved, putative carboxylesterase (referred to as yvaK in Bacillus subtilis) at the molecular and cellular level. First, phenotypic characterization of fphH-deficient transposon mutants revealed phenotypes during growth under nutrient deprivation, biofilm formation, and intracellular survival. Biochemical and structural investigations revealed that FphH acts as an esterase and lipase based on a fold well suited to act on a small to long hydrophobic unbranched lipid group within its substrate and can be inhibited by active site-targeting oxadiazoles. Prompted by a previous observation that fphH expression was upregulated in response to fusidic acid, we found that FphH can deacetylate this ribosome-targeting antibiotic, but the lack of FphH function did not infer major changes in antibiotic susceptibility. In conclusion, our results indicate a functional role of this hydrolase in S. aureus stress responses, and hypothetical functions connecting FphH with components of the ribosome rescue system that are conserved in the same gene cluster across Bacillales are discussed. Our atomic characterization of FphH will facilitate the development of specific FphH inhibitors and probes to elucidate its physiological role and validity as a drug target.

Recent advances and challenges in antibacterial drug development: Editorial

Editorial