title: Analysis of the unique structural and physicochemical properties of the DraD/AfaD invasin in the context of its belonging to the family of chaperone/usher type fimbrial subunits.
abstract: BACKGROUND
  DraD invasin encoded by the dra operon possesses a classical structure characteristic to fimbrial subunits of the chaperone/usher type. The Ig-fold of the DraD possesses two major characteristics distinguishing it from the family of fimbrial subunits: 1) a distortion of the β-barrel structure in the region of the acceptor cleft, demonstrated by a disturbance of the main-chain hydrogen bonds network, and 2) an unusually located disulfide bond connecting B and F strands - the localization exclusively observed in the subfamily of DraD/AfaD-type subunits.
  
  
  RESULTS
  To evaluate the influence of the DraD-sc specific structural features on its stability and mechanism of thermal denaturation, a series of DSC and FT-IR denaturation experiments were performed giving following conclusions. 1) The DraD-sc is characterized by a low stability (standard Gibbs free energy and enthalpy of unfolding of 18.4 ±1.4 kJ mol(-1) and 131 ±25 kJ mol(-1), respectively) that contrasts strongly with almost infinite stability of the described previously DraE-sc fimbrial protein. 2) The DraD-sc unfolds thermally according to the two state equilibrium model, in contrast to the irreversible kinetically controlled transition of the DraE-sc. 3) The DraD specific disulfide bond is crucial at the folding stage and has little stability effect in the mature protein.
  
  
  CONCLUSIONS
  Data published so far emphasize unique biological properties of the DraD invasin as fimbrial subunit: a chaperone independent folding, an usher independent surface localization and the possibility to exist in two forms: as unbound subunits and as loosely bound at fimbrial tip.Presented calorimetric and FT-IR stability data combined with structural correlations has underlined that the DraD invasin is also characterized by unique physicochemical and structural attributes in the context of its belonging to the family of fimbrial subunits.
authors.affiliation: Department of Microbiology, Gdańsk University of Technology, ul, Narutowicza 11/12, 80-233 Gdańsk, Poland. rafpiate@pg.gda.pl
authors.forename: Rafał J
authors.initials: RJ
authors.lastname: Piątek
authors.forename: Piotr
authors.initials: P
authors.lastname: Bruździak
authors.forename: Beata M
authors.initials: BM
authors.lastname: Zalewska-Piątek
authors.forename: Marek A
authors.initials: MA
authors.lastname: Wojciechowski
authors.forename: Justyna M
authors.initials: JM
authors.lastname: Namieśnik
authors.forename: Józef W
authors.initials: JW
authors.lastname: Kur
mesh_terms: D018830:Adhesins, Escherichia coli / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D004220:Disulfides; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry*; D036781:Fimbriae Proteins / Q000737:chemistry*; D010861:Fimbriae, Bacterial / Q000378:metabolism; D018832:Molecular Chaperones / Q000737:chemistry*; D011489:Protein Denaturation; D017510:Protein Folding; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D018830:Adhesins, Escherichia coli; C108510:AfaD protein, E coli; D004220:Disulfides; C530426:DraD invasin, E coli; D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; D036781:Fimbriae Proteins