Competitive Profiling of Ligandable Cysteines in Staphylococcus aureus with an Organogold Compound

With the idea of exploiting metal-templated reactions to achieve selective modification of cysteines in proteins for antibacterial applications, an organometallic cyclometalated Au(III) compound was explored in a competitive chemoproteomic approach based on the isoDTB-ABPP (isotopically labelled desthiobiotin azide-activity-based protein profiling) technology in S. aureus cell extracts. In this way, more than 100 ligandable cysteines where identified, of which 10 were close to functional sites of proteins encoded by essential genes indicating potential for antibiotic development. Interestingly, more than 50% of the identified ligandable sites were not engaged by organic α-chloroacetamides in a previous study, indicating that organometallic compounds expand the ligandable space in bacteria. A selected interaction identified by isoDTB-ABPP was validated using an enzyme activity assay, and intact protein mass spectrometry showed that cysteine arylation of an unprecedented target occurs with the studied compound. The obtained results constitute the proof-of-concept that this family of organogold compounds has potential for therapeutic protein targeting via selective, covalent modification of cysteine residues in bacteria. Looking more broadly, our study demonstrates that the targets of cyclometalated gold compounds can be studied proteome-wide with competitive residue-specific chemoproteomics enabling the expansion of the known ligandable proteome to sites that can be addressed with this compound class.