Medical Microbiology and Hospital Epidemiology 


Research Group Dr. Wolfgang Fischer

The research group of Wolfgang Fischer is engaged in elucidating the molecular mechanisms of action of type IV protein secretion systems in the human pathogen Helicobacter pylori, the causative agent of diseases such as chronic gastritis, duodenal ulcers, or gastric cancer. Two major ways how these bacteria utilize such systems are the direct modulation of infected host cells by effector molecules, and the exchange of genetic material in the process of horizontal gene transfer. Specifically, the Cytotoxin-associated gene (Cag) type IV secretion system and its translocated effector protein CagA are well-established pathogenicity determinants of H. pylori, notably for the development of gastric cancer. One of our research aims is to understand the type IV secretion process of the CagA protein in mechanistic detail. A second focus of our work is to examine integrating and conjugative elements (ICEs), genome islands which may use type IV secretion systems for horizontal DNA transfer, and which have the potential for providing additional host-interaction factors to individual H. pylori strains.

The Research Group

Chair

Dr. Wolfgang Fischer

Wolfgang Fischer is a Group Leader in the Department of Medical Microbiology and Hospital Epidemiology at the Max von Pettenkofer Institute of Ludwig Maximilian University (LMU) in Munich, Germany. He studied Chemistry at the Universities of Saarbrücken and Freiburg, and obtained his doctoral degree in Biochemistry at the University of Tübingen. Following a postdoctoral fellowship at the Max Planck Institute for Biology in Tübingen, he joined the Max von Pettenkofer Institute in 1997, where he completed his habilitation in 2005. Since 2003, he holds a Research Associate/Group Leader position at the Max von Pettenkofer Institute. His research interests are bacterial protein secretion, molecular mechanisms of infectious diseases, and mobile genetic elements.

Dr. Wolfgang Fischer

Group Members

Current members

Wolfgang Fischer, Dr. rer. nat.
E-Mail: fischer@mvp.lmu.de
Phone: +49 89 2180-72877

Mrinalini Srinivasan, M. Sc.
E-Mail: srinivasan@mvp.lmu.de
Phone: +49 89 2180-72920

 

Research

Functional analysis of the H. pylori Cag type IV secretion apparatus

The Cag type IV secretion system, which is encoded on the cag pathogenicity island (cagPAI), is considered a major virulence factor of H. pylori. Important functions of this secretion system are the induction of a proinflammatory response in gastric tissues, and direct translocation of the bacterial CagA protein into the cytoplasm of different host cell types. Once inside the target cell, CagA is modified by tyrosine phosphorylation, and causes changes in cell morphology and gene expression. The Cag type IV secretion system uses at least 15 different proteins to form a secretion apparatus spanning both bacterial membranes, and pilus-like appendages at the bacterial surface. We have previously identified protein-protein interactions among several components of the secretion apparatus, including a subcomplex formed by the unique integrin-binding components CagI and CagL together with an additional protein involved in pilus formation, CagH. We are working on a further molecular characterization of such subcomplexes, using genetic, cell biological and biochemical techniques.

Signal recognition and secretion dynamics in the Cag type IV secretion system

The precise, but dynamic sorting of proteins to their respective destinations is a process of fundamental importance for all living cells. In the case of CagA targeting to the type IV secretion apparatus, our studies have shown that the secretion chaperone CagF binds to several domains of its interaction partner CagA, and thereby probably keeps CagA in a translocation-competent state. Furthermore, a complex of the CagA-dedicated translocation factors Cagβ and CagZ appears to form a type IV substrate recognition complex associated with the bacterial cytoplasmic membrane. We have recently developed novel reporter assays to monitor type IV secretion in H. pylori in a quantitative manner, and we have used them to examine molecular parameters of the secretion process, such as the requirement of protein unfolding, or secretion signals that target CagA to the type IV secretion apparatus. Kinetic measurements of CagA transport into target cells have demonstrated a fast onset of translocation after physical contact between bacterial and host cells, but also a rapid saturation, leaving a substantial fraction of bacterial CagA pools untranslocated.

A detailed knowledge about such protein interactions and early molecular steps of translocation is not only important for understanding H. pylori pathogenicity and the physiology of type IV secretion systems in general, but it may also be useful to develop specific inhibitory drugs.

Integrating conjugative elements (ICEs) as mobile genome islands in H. pylori

One of the most remarkable features of H. pylori is its unusual genetic diversity, resulting from high mutation and recombination rates as well as from efficient horizontal gene transfer mechanisms. In addition, mobile genetic elements, such as plasmids, phages, or integrating conjugative elements (ICEs) strongly contribute to genome variability between different isolates. Two related types of ICEs, termed ICEHptfs3 and ICEHptfs4, can be distinguished in H. pylori strains. Both types of genome islands harbour between 30 and 40 genes encoding type IV secretion (conjugation) systems and DNA-processing functions, but also variable sets of potential cargo genes. The function of these elements in bacterial physiology or host interaction is currently unknown, but the presence of certain ICE genes has been associated with disease development. Comparative genome analysis of H. pylori strains, as well as genetic studies using model strains, has revealed that ICEs can insert via site-specific recombination into the bacterial chromosome, using short integration motifs, and are thus capable of integrating at variable chromosomal loci. We have demonstrated excision from the chromosome at low rates, and efficient horizontal transfer to recipient strains by a non-classical transfer mechanism that involves homologous recombination for ICE integration.O

Publications

Top 10 Publications

Steiner TM, Lettl C, Schindele F, Goebel W, Haas R, Fischer W* & Eisenreich W* (2021) Substrate usage determines carbon flux via the citrate cycle in Helicobacter pylori. Mol Microbiol 116: 841 (doi:10.1111/mmi.14775). (*, corr. Authors)
Lettl C, Haas R & Fischer W (2021) Kinetics of CagA type IV secretion by Helicobacter pylori and the requirement for substrate unfolding. Mol Microbiol 116: 794 (doi: 10.1111/mmi.14772).
Weiss E, Spicher C, Haas R & Fischer W (2019) Excision and transfer of an integrating and conjugative element in a bacterial species with high recombination efficiency. Sci Rep 9: 8915 (doi: 10.1038/s41598-019-45429-z).
Zhao Q, Busch B, Jiménez-Soto LF, Ishikawa-Ankerhold H, Massberg S, Terradot L, Fischer W & Haas R (2018) Integrin but not CEACAM receptors are dispensable for Helicobacter pylori CagA translocation. PLoS Pathog 14: e1007359 (doi: 10.1371/journal.ppat.1007359).
Königer V, Holsten L, Harrison U, Busch B, Loell E, Zhao Q, Bonsor DA, Roth A, Kengmo-Tchoupa A, Smith SI, Mueller S, Sundberg EJ, Zimmermann W, Fischer W, Hauck CR & Haas R (2016) Helicobacter pylori exploits human CEACAMs via HopQ for adherence and translocation of CagA. Nat Microbiol 2: 16188 (doi: 10.1038/nmicrobiol.2016.233).
Schindele F, Weiss E, Haas R & Fischer W (2016) Quantitative analysis of CagA type IV secretion by Helicobacter pylori reveals substrate recognition and translocation requirements. Mol Microbiol 100: 188 (doi: 10.1111/mmi.13309).
Jurik A, Haußer E, Kutter S, Pattis I, Praßl S, Weiss E & Fischer W (2010) The coupling protein Cagβ and its interaction partner CagZ are required for type IV secretion of the Helicobacter pylori CagA protein. Infect Immun 78: 5244.
Fischer W, Windhager L, Rohrer S, Zeiller M, Karnholz A, Hoffmann R, Zimmer R & Haas R (2010) Strain-specific genes of Helicobacter pylori: Genome evolution driven by a novel type IV secretion system and genomic island transfer. Nucleic Acids Res 38: 6089.
Hohlfeld S, Pattis I, Püls J, Plano GV, Haas R & Fischer W (2006) A C-terminal secretion signal is necessary, but not sufficient for type IV secretion of the Helicobacter pylori CagA protein. Mol Microbiol 59: 1624.
Odenbreit S, Püls J, Sedlmaier B, Gerland E, Fischer W & Haas R (2000) Translocation of Helicobacter pylori CagA into gastric epithelial cells by type IV secretion. Science 287: 1497.