Aileen Harrer


B10 Molecular functions and signal transduction of the serine protease htrA, a novel secreted effector protein of bacterial pathogens

Principal investigator
Steffen Backert

Heinrich Sticht

Identification of a consensus cleavage motif by serine protease HtrA of the gastrointestinal pathogens Campylobacter jejuni and Helicobacter pylori and search for novel host cell targets

The epithelium of mammalian body surfaces is formed by layers of polarized cells, and represents the first natural barrier both for commensals and intruding pathogens. This barrier is controlled by the tight and adherens junctions, which form highly organized protein complexes. Our group is interested in the molecular mechanisms how various gastrointestinal pathogens manipulate these junctions for travelling across the epithelial barrier resulting in disease-associated processes.

Campylobacter jejuni and Helicobacter pylori are the most important gastrointestinal pathogens worldwide. Crossing the host intestinal epithelial barrier, release of effectors, receptor targeting and cellular invasion have been reported as primary reasons for tissue damage triggered by these pathogens, but the molecular mechanisms are widely unknown. The serine protease HtrA (High temperature resistant protein A) of both pathogens is important for stress tolerance and protein quality control in the periplasm (Fig. 1). However, we found that HtrA can be also secreted into the extracellular space, where it cleaves the major adherens junction protein E-cadherin and probably other host cell factors (Hoy et al., 2010, 2012; Boehm et al., 2012). The extracellular NTF-domain of E-cadherin is cleaved into various fragments, which are released in the cell culture supernatant. We investigated the cleavage patterns of HtrA in E‑cadherin. Using mass spectrometry analyses and Edman sequencing we determined a consensus cleavage motif ([VITA]↓[VITA]-x-x-D-[DN]) of HtrA in four signature sites of E-cadherin (Schmidt et al., 2016, submitted). The tight junctions are other important structures and located above the adherens junctions, which seal the intercellular space between two or more neighbouring cells for maintaining epithelial cell polarity and avoid leakage of metabolites. Thus, before targeting the E-cadherin-based adherens junctions, the pathogens must overcome the tight junctions. We consequently proposed that secreted HtrA may also target one or more tight junction proteins, work which is currently in progress by using bioinformatics and proteomics approaches.


Figure:Architecture and function of HtrA proteases. (A) Schematic representation of the domain organization of HtrA family proteases. The protease domain is shown in light blue, PDZ-1 and PDZ-2 domains in green, three conserved amino acid residues (HDS, histidine, aspartate and serine) in the active centre in yellow, SS (signal sequence) is shown in purple, TM (transmembrane domain) as grey squares, IGFBP (Insulin-like growth factor binding) in pink, KI (Kazal protease inhibitor domain) as dark blue and IAP (inhibitor of apoptosis protein domain) in orange. For individual HtrA proteins, Ec represents Escherichia coli, Cj: Campylobacter jejuni, Hp: Helicobacter jejuni, h: Homo sapiens, Mt: Mycobacterium tuberculosis and At: Arabidopsis thaliana. (B) The combination of a protease domain (the active site is highlighted in yellow) and a PDZ domain generates complex proteolytic assemblies in which the PDZ domain exerts a multitude of different functions. The PDZ domain (green) may be involved in substrate or effector molecule binding (dark blue), regulation of protease function (indicated by the green extension protruding towards the protease domain) and oligomerization or cellular localization of the PDZ protease as indicated.





October 2016 8th Annual Retreat, Erlangen School of Molecular Communication, Schloss Schney, Lichtenfels, Germany
”The impact of Campylobacter jejuni and Helicobacter pylori serine protease HtrA on tight junctions”
October 2015 2nd International SFB 796 Conference: Mechanisms of microbial host cell manipulation: From plants to humans, Erlangen, Germany
”Identification of a consensus cleavage motif by serin protease HtrA of the gastrointestinal pathogens Campylobacter jejeuni and Helicobacter pylori and search for novel host cell targets”
July 2015 7th Annual Retreat, Erlangen School of Molecular Communication, Schloss Hirschberg, Beilngries, Germany
”The impact of serine protease HtrA towards tight junction proteins during infection of host cells with the gastrointestinal pathogens Campylobacter jejuni and Helicobacter pylori