title: The Mycobacterium tuberculosis chaperonin 10 monomer exhibits structural plasticity.
abstract: The conditions which favor dissociation of oligomeric Mycobacterium tuberculosis chaperonin 10 and the solution structure of the monomer were studied by analytical ultracentrifugation, size exclusion chromatography, fluorescence, and circular dichroism spectroscopies. At neutral pH and in the absence of divalent cations, the protein is fully monomeric below approximately a 4.7 microM concentration. Under these conditions the monomer forms completely unfolded and partially folded conformers which are in equilibrium with each other. One conformer accumulates over the others which is stable within a very narrow range of temperatures. It contains a beta-sheet-structured C-terminal half and a mostly disordered N-terminal half. Other components of the equilibrium include partially helical structures which do not completely unfold at high temperature or under strong acidic conditions. Complete unfolding of the monomer occurs in the presence of denaturants or below 14 degrees C. Cold-denaturation is detected at an unusually high temperature and this may be due to the concentration of hydrophobic residues, which is larger in chaperonins than in other globular proteins. Finally, the monomer self-associates in the pH range 5.8-2.9, where it forms small oligomers. A structure-activity relationship was investigated with the sequences known to be involved in the various biological activities of the monomer.
authors.affiliation: Italfarmaco Research Centre, via Lavoratori 54, Cinisello Balsamo 20092 Milan, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Fossati
authors.forename: Pietro
authors.initials: P
authors.lastname: Cremonesi
authors.forename: Gaetano
authors.initials: G
authors.lastname: Izzo
authors.forename: Emanuele
authors.initials: E
authors.lastname: Rizzi
authors.forename: Giovanni
authors.initials: G
authors.lastname: Sandrone
authors.forename: Stephen
authors.initials: S
authors.lastname: Harding
authors.forename: Neil
authors.initials: N
authors.lastname: Errington
authors.forename: Christopher
authors.initials: C
authors.lastname: Walters
authors.forename: Brian
authors.initials: B
authors.lastname: Henderson
authors.forename: Michael M
authors.initials: MM
authors.lastname: Roberts
authors.forename: Anthony R M
authors.initials: AR
authors.lastname: Coates
authors.forename: Paolo
authors.initials: P
authors.lastname: Mascagni
mesh_terms: D018835:Chaperonin 10 / Q000737:chemistry* / Q000378:metabolism; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D009169:Mycobacterium tuberculosis / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013696:Temperature; D014461:Ultracentrifugation
chemical_list: D018835:Chaperonin 10