Helmholtz-OCPC-Program (2021-2023): Structural Insight into the Human Zonulin, a Prehaptoglogin-2 Protein in Celiac Disease.

Motivation

Celiac disease (CeD), is a chronic intestinal immune-mediated disease caused by exposure to dietary gluten, which is a storage protein in wheat, rye and barley. Gluten has ability to resist proteolytic breakdown by gastric, pancreatic, and intestinal digestive proteases due to its high proline content, and produces non-digested gliadin polypeptides. In CeD, these non-digested gliadin polypeptides cross to intestinal submucosa and cause an abnormal immune response leading to inflammatory reaction in small bowl. Untreated, this leads to malnutrition, higher risk of cancer and shortened life expectation. There is no cure and no medication available to date, the only form of treatment is gluten-free diet for lifetime. To facilitate drug development for CeD, we aim to study the molecular mechanisms involved by macromolecular crystallography.

An important step in the pathogeneiss of CeD is the gliadin-induced zonulin release in transcellular passage. Zonulin is as a regulatory marker of intercellular tight junctions (TJ). When stimulated by the gluten, the release of zonulin will increase, and then zonulin induces transactivation of epidermal growth factor receptor (EGFR) by protease-activated receptor (PAR2) leading to small intestine TJ disassembly. Zonulin is identified as a single chain pre-haptoglobin 2, consist of light α unit and heavy β unit. which has signal peptide (1-18), α chain (19-160) (α1 (31 – 88)) and α2 (90 -147), β chain (162-406).

When the zonulin is converted into mature form by cell tryptase IV, the function of loosening tight junction (TJ) is lost. The mature form binds hemoglobin (Hb) in blood plasma to form stable Hp-Hb complexes thereby preventing Hb-induced oxidative tissue damage. To so far, Hp is demonstrated that it is αβ dimer, which contains a complement control protein (CCP) domain and a serine protease-like (SP) region.

In this study, we aim to determine the structure of intact pre-haptoglobin 2 (zonulin) to better understand the differences in function of pre and mature form and provide structural details to aid rational drug design.

 

 

References

1. The Oslo definitions for coeliac disease and related terms; Ludvigsson JF et al.; Gut. 2013; DOI: 10.1136/gutjnl-2011-301346.

2. Zonulin and its regulation of intestinal barrier function: the biological door to inflammation, autoimmunity, and cancer; Fasano A; Physiol. Rev. 2011; DOI: 10.1152/physrev.00003.2008.

3. Identification of human zonulin, a physiological modulator of tight junctions, as prehaptoglobin-2; Tripathia A et al.; Proc. Natl. Acad. Sci. 2009; .DOI: 10.1073/pnas.0906773106.

4. Haptoglobin as a biomarker; Naryzhny Snn et al.; Biochem. Mosc. Suppl. B Biomed. Chem. 2021; DOI: 10.1134/S1990750821030069.

 

 

Post-doctoral researcher: Jialing Song (DESY and University of Science and Technology of China)

Staff of P11-High-Throughput Macromolecular Crystallography Beamline:

Spyros Chatziefthymiou, Johanna Hakanpää

Collaborators:

Susanne Witt (CSSB Protein Production Facility, Hamburg).

Professor Tengchuang Jin (University of Science and Technology of China).