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Structural Insights into Polymorphic ABO Glycan Binding by Helicobacter pylori
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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2016 (English)In: Cell Host and Microbe, ISSN 1931-3128, E-ISSN 1934-6069, Vol. 19, no 1, 55-66 p.Article in journal (Refereed) PublishedText
Abstract [en]

The Helicobacter pylori adhesin BabA binds mucosal ABO/Le b blood group (bg) carbohydrates. BabA facilitates bacterial attachment to gastric surfaces, increasing strain virulence and forming a recognized risk factor for peptic ulcers and gastric cancer. High sequence variation causes BabA functional diversity, but the underlying structural-molecular determinants are unknown. We generated X-ray structures of representative BabA isoforms that reveal a polymorphic, three-pronged Le(b) binding site. Two diversity loops, DL1 and DL2, provide adaptive control to binding affinity, notably ABO versus O bg preference. H. pylori strains can switch bg preference with single DL1 amino acid substitutions, and can coexpress functionally divergent BabA isoforms. The anchor point for receptor binding is the embrace of an ABO fucose residue by a disulfide-clasped loop, which is inactivated by reduction. Treatment with the redox-active pharmaceutic N-acetylcysteine lowers gastric mucosal neutrophil infiltration in H. pylori-infected Le(b)-expressing mice, providing perspectives on possible H. pylori eradication therapies.

Place, publisher, year, edition, pages
2016. Vol. 19, no 1, 55-66 p.
National Category
Cell and Molecular Biology
Identifiers
URN: urn:nbn:se:umu:diva-117839DOI: 10.1016/j.chom.2015.12.004ISI: 000369839900010PubMedID: 26764597OAI: oai:DiVA.org:umu-117839DiVA: diva2:916716
Available from: 2016-04-04 Created: 2016-03-04 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.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1813
Keyword
Helicobacter pylori
National Category
Microbiology in the medical area
Research subject
Medical Biochemistry
Identifiers
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)
Opponent
Supervisors
Funder
The Kempe Foundations
Available from: 2016-05-19 Created: 2016-05-16 Last updated: 2016-05-26Bibliographically approved

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Gideonsson, PärBugaytsova, JeannaMendez, MelissaNordén, JennyFallah, MahsaRakhimova, LenaShevtsova, AnnaBrännström, KristofferNy, TorArnqvist, AnnaBorén, Thomas
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