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A Repetitive DNA Element Regulates Expression of the Helicobacter pylori Sialic Acid Binding Adhesin by a Rheostat-like Mechanism
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
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2014 (English)In: PLoS Pathogens, ISSN 1553-7366, E-ISSN 1553-7374, Vol. 10, no 7, e1004234Article in journal (Refereed) Published
Abstract [en]

During persistent infection, optimal expression of bacterial factors is required to match the ever-changing host environment. The gastric pathogen Helicobacter pylori has a large set of simple sequence repeats (SSR), which constitute contingency loci. Through a slipped strand mispairing mechanism, the SSRs generate heterogeneous populations that facilitate adaptation. Here, we present a model that explains, in molecular terms, how an intergenically located T-tract, via slipped strand mispairing, operates with a rheostat-like function, to fine-tune activity of the promoter that drives expression of the sialic acid binding adhesin, SabA. Using T-tract variants, in an isogenic strain background, we show that the length of the T-tract generates multiphasic output from the sabA promoter. Consequently, this alters the H. pylori binding to sialyl-Lewis x receptors on gastric mucosa. Fragment length analysis of post-infection isolated clones shows that the T-tract length is a highly variable feature in H. pylori. This mirrors the host-pathogen interplay, where the bacterium generates a set of clones from which the best-fit phenotypes are selected in the host. In silico and functional in vitro analyzes revealed that the length of the T-tract affects the local DNA structure and thereby binding of the RNA polymerase, through shifting of the axial alignment between the core promoter and UP-like elements. We identified additional genes in H. pylori, with T- or A-tracts positioned similar to that of sabA, and show that variations in the tract length likewise acted as rheostats to modulate cognate promoter output. Thus, we propose that this generally applicable mechanism, mediated by promoter-proximal SSRs, provides an alternative mechanism for transcriptional regulation in bacteria, such as H. pylori, which possesses a limited repertoire of classical trans-acting regulatory factors.

Place, publisher, year, edition, pages
2014. Vol. 10, no 7, e1004234
National Category
Physiology Physical Chemistry
URN: urn:nbn:se:umu:diva-91641DOI: 10.1371/journal.ppat.1004234ISI: 000340551000026PubMedID: 24991812OAI: diva2:737526
Available from: 2014-08-13 Created: 2014-08-13 Last updated: 2016-05-18Bibliographically approved
In thesis
1. Helicobacter pylori: molecular insights into regulation of adhesion properties
Open this publication in new window or tab >>Helicobacter pylori: molecular insights into regulation of adhesion properties
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Helicobacter pylori infects the human stomach and triggers an inflammatory response that damages the gastric tissue. This host-pathogen interplay has dire consequences as up to 20 % of infected individuals develop peptic ulcer disease or gastric cancer. Given that half of the world’s population is infected, the number of afflicted humans is staggering and also tells that H. pylori is extremely efficient in spreading and maintaining infection. To enable persistent infection many factors play a role, but one important feature of H. pylori is its impressive ability to adhere to the slimy gastric mucus layer and the underlying epithelial cells. This occurs mainly via the BabA and SabA proteins that bind ABO/Leb- and sLex/sLea-antigens. I have in my thesis studied how these two proteins are utilized and regulated.

H. pylori transcription is in part controlled by two-component systems (TCSs) that use a sensor protein and a DNA-binding response regulator. We have studied how these systems control sabA and to some extent babA and indeed found a better map of how sabA and babA is regulated at the transcriptional level. We also found that variations in a polynucleotide T-tract located in the sabA promotor could fine-tune SabA expression/ sLex-binding. Thus we have exposed how strict regulation by TCSs combined with stochastic processes together shapes attachment in the bacterial population.

As the buffering mucus layer is constantly exfoliated, placing H. pylori in bactericidal acid, we hypothesized that low pH should abrogate adhesion. SabA expression was indeed repressed in low pH, however BabA expression remained unaffected. The BabA/ Leb-binding was instead directly reversibly hampered by low pH and the degree of pH sensitivity was strain dependent and encoded in the BabA sequence. We believe that the pH dependent loss of binding is one key factor H. pylori utilizes to maintain persistent infection.

BabA is divided in generalists that bind ABO antigens and specialists that only bind blood group (bg) O. We co-crystalized BabA bound to these receptors and established the structural basis for generalist vs. specialist discrimination. We furthermore found a disulfide-clasped loop (CL2) in the center of the binding domain crucial for binding. Breaking CL2 with N-Acetylcysteine (NAC) disrupted binding and H. pylori infection mice experiments revealed inflammatory reduction upon NAC-treatment.

In sum, I have in my thesis dissected how H. pylori controls its adhesive abilities and how intrinsic properties in binding can be exploited for therapeutic purposes.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2016. 53 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1813
Helicobacter pylori
National Category
Microbiology in the medical area
Research subject
Medical Biochemistry
urn:nbn:se:umu:diva-120466 (URN)978-91-7601-493-6 (ISBN)
Public defence
2016-06-09, N300, Umeå universitet, Naturvetarhuset, Umeå, 09:00 (English)
The Kempe Foundations
Available from: 2016-05-19 Created: 2016-05-16 Last updated: 2016-05-26Bibliographically approved

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Åberg, AnnaGideonsson, PärVallström, AnnaOlofsson, AnnelieÖhman, CarinaRakhimova, LenaBorén, ThomasBrännström, KristofferArnqvist, Anna
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