Kingella kingae is a member of the commensal oropharyngeal flora of young children. Improvements in detection methods have led to the recognition of K. kingae as an emerging pathogen that frequently causes osteoarticular infections in children and a severe form of infective endocarditis in children and adults. Kingella kingae secretes a membrane-damaging RTX (Repeat in ToXin) toxin, RtxA, which is implicated in the development of clinical infections. However, the mechanism by which RtxA recognizes and kills host cells is largely unexplored. To facilitate structure-function studies of RtxA, we have developed a procedure for the overproduction and purification of milligram amounts of biologically active recombinant RtxA. Mass spectrometry analysis revealed the activation of RtxA by post-translational fatty acyl modification on the lysine residues 558 and/or 689 by the fatty-acyltransferase RtxC. Acylated RtxA was toxic to various human cells in a calcium-dependent manner and possessed pore-forming activity in planar lipid bilayers. Using various biochemical and biophysical approaches, we demonstrated that cholesterol facilitates the interaction of RtxA with artificial and cell membranes. The results of analyses using RtxA mutant variants suggested that the interaction between the toxin and cholesterol occurs via two cholesterol recognition/interaction amino acid consensus motifs located in the C-terminal portion of the pore-forming domain of the toxin. Based on our observations, we conclude that the cytotoxic activity of RtxA depends on post-translational acylation of the K558 and/or K689 residues and on the toxin binding to cholesterol in the membrane.

Department of Chemical and Biomolecular Engineering Lehigh University Bethlehem PA USA

Department of Orofacial Sciences and Program in Craniofacial Biology University of California San Francisco CA USA

Department of Pathology School of Dental Medicine University of Pennsylvania Philadelphia PA USA

Faculty of Science Charles University Prague Czech Republic

Institute of Microbiology of the CAS v v i Prague Czech Republic

The Department of Cell and Molecular Biology at Karolinska Institutet Stockholm Sweden

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Kingella kingae RtxA Cytotoxin in the Context of Other RTX Toxins

Different roles of conserved tyrosine residues of the acylated domains in folding and activity of RTX toxins

Binding of Kingella kingae RtxA Toxin Depends on Cell Surface Oligosaccharides, but Not on β2 Integrins

Acyltransferase-mediated selection of the length of the fatty acyl chain and of the acylation site governs activation of bacterial RTX toxins

Rapid Purification of Endotoxin-Free RTX Toxins