title: Characterization of oligomeric assembly of colonization factor CS6 from enterotoxigenic Escherichia coli.
abstract: The widely distributed colonization factor (CF) CS6 of enterotoxigenic Escherichia coli (ETEC) has gained importance over the years in terms of its structure and function. CS6 is an afimbrial assembly in contrast to the other ETEC CFs, which are mostly fimbrial. A recent study predicted a linear fibre model for recombinant chimeric CS6 and formation of oligomers in solution. In this study, we characterized the oligomeric assembly of CS6, purified from a clinical ETEC isolate and identified its existence in the WT strain. We found that purified CS6 forms a continuous array of higher order oligomers composed of two tightly associated subunits, CssA and CssB in an equal (1:1) stoichiometry. This oligomerization occurs by formation of (CssA-CssB)n complex where 'n' increases with the concentration. The diameter of CS6 oligomers also proportionally increases with concentration. More significantly, we showed CS6 oligomers to be spherical in shape instead of being linear fibres as predicted earlier and this was further confirmed by electron microscopy. We also showed CS6 assembled on the bacterial surface in the form of an oligomeric complex. This process depends on the expression of properly folded CssA and CssB together, guided by the chaperone CssC and usher CssD. In conclusion, our results provide evidence for the existence of concentration-dependent, spherical oligomers of CS6 comprising both the structural subunits in equal stoichiometry and the CS6 oligomeric complex on the ETEC surface.
authors.affiliation: National Institute of Cholera and Enteric Diseases, Kolkata, India.
authors.forename: Subrata
authors.initials: S
authors.lastname: Sabui
authors.affiliation: National Institute of Cholera and Enteric Diseases, Kolkata, India.
authors.forename: Anusuya
authors.initials: A
authors.lastname: Debnath
authors.affiliation: National Institute of Cholera and Enteric Diseases, Kolkata, India.
authors.forename: Abhisek
authors.initials: A
authors.lastname: Ghosal
authors.affiliation: National Center for Global Health and Medicine, Tokyo, Japan.
authors.forename: Takeaki
authors.initials: T
authors.lastname: Wajima
authors.affiliation: National Center for Global Health and Medicine, Tokyo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Hamabata
authors.affiliation: National Institute of Cholera and Enteric Diseases, Kolkata, India.
authors.forename: T
authors.initials: T
authors.lastname: Ramamurthy
authors.affiliation: National Institute of Cholera and Enteric Diseases, Kolkata, India.
authors.forename: A N
authors.initials: AN
authors.lastname: Ghosh
authors.affiliation: Saha Institute of Nuclear Physics, Kolkata, India.
authors.forename: Soumen
authors.initials: S
authors.lastname: Basak
authors.affiliation: National Institute of Cholera and Enteric Diseases, Kolkata, India.
authors.forename: Nabendu Sekhar
authors.initials: NS
authors.lastname: Chatterjee
mesh_terms: D000942:Antigens, Bacterial / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D054307:Enterotoxigenic Escherichia coli / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004927:Escherichia coli Infections / Q000382:microbiology*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans
chemical_list: D000942:Antigens, Bacterial; C098406:CS6 antigen, E coli; D029968:Escherichia coli Proteins