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

BackgroundDraD 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.ResultsTo 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.ConclusionsData 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.

PI3K/Akt pathway restricts epithelial adhesion of Dr+Escherichia coliby down-regulating the expression of decay accelerating factor

“…Dr adhesins are a conserved family of gram negative bacterial adhesion proteins and they are assembled via chaperone-usher pathway (11). The biogenesis of Dr adhesins at the structural and molecular level is well known (12–15). However, the mechanisms of interactions between Dr + E. coli and host cells that are crucial for bacterial pathogenesis are much less known.…”

“…11 The biogenesis of Dr adhesins at the structural and molecular level is well known. [12][13][14][15] However, the mechanisms of interactions between Dr þ E. coli and host cells that are crucial for bacterial pathogenesis are much less known. Previous studies in our laboratory have shown that nitric oxide (NO) down-regulates the DAF expression in a dose-and time-dependent manner in an endometrial epithelial cell line.…”

Pathogenesis of Human Diffusely Adhering Escherichia coli Expressing Afa/Dr Adhesins (Afa/Dr DAEC): Current Insights and Future Challenges

“…In the case of the E subunit, two conserved cysteine residues forming a disulfide bond are important for stabilizing elements of the immunoglobulin fold of the Dr fimbriae. With regard to the DraD subunit (179), it has been reported that when the DraE subunit assembles, the DraD subunit localizes at the tip of the fiber (158,159,166,167,180). Jedrzejczak et al (181) have shown that the DraD subunit localizes at the tip, because it lacks a donor strand and as a consequence functions only as an acceptor.…”

“…It has been proposed by Le Bouguénec and coworkers (357) that the D adhesin subunits encoded by the dra, daa, and afa-1 to -3 operons function as an invasin for the entry of Afa/Dr DAEC into urothelial and bladder cells. DraD and AfaD adhesin subunits have been identified at the tips of Afa/Dr fibrils (167,180). AfaD protein, unlike the AfaE protein, was able to detach from the bacterium (28,168,169).…”