Common thraot bacteria
Found to cause
by produceing lysine
that binds to cholesterol
with toxic results to human cells
Emerg Microbes Infect. 2018; 7: 178.
Published online 2018 Nov 7. doi: 10.1038/s41426-018-0179-x
Cytotoxic activity of Kingella kingae RtxA toxin depends on post-translational acylation of lysine residues and cholesterol binding
Adriana Osickova,#1,2 Nataliya Balashova,#3 Jiri Masin,1 Miroslav Sulc,1,2 Jana Roderova,1 Tomas Wald,1,5 Angela C. Brown,4 Evan Koufos,4 En Hyung Chang,4 Alexander Giannakakis,3,6 Edward T. Lally,3 and Radim Osickacorresponding author#1
Kingella kingae is a member of the commensal oropharyngeal [throat] flora of young children. Improvements in detection methods have led to the recognition of K. kingae as an emerging pathogen that frequently causes osteoarticular [bone and joint] infections in children and a severe form of infective endocarditis [inner heart and valve] 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.
Further in the full article:
We demonstrated that similar to RtxA secreted by K. kingae11, the highly purified recombinant RtxA [lipid lysine] is a potent cytotoxin capable of rapid and efficient killing of various human cell types.
commensal: [ kŏ-men´sal ]
1. living on or within another organism, and deriving benefit without harming or benefiting the host individual.
2. a parasitic organism that causes no harm to the host. [or so thought]