Prof. Dr. Matthias Leippe
- Secretary -
A major concern of Zoophysiology is to compare the complex mechanisms that various species from different parts of the animal phylogeny use to function – from the level of the organism down to the level of the molecule. Our research is concerned with comparative immunobiology and molecular parasitology.
are studying the evolution of the immune systems by comparing well-established
model systems such as the free-living amoeboid protozoon Dictyostelium
discoideum and the nematode Caenorhabditis elegans, and,
in addition, marine invertebrates.
are elucidating the other side of host-pathogen interactions by investigating
molecularly pathogenicity mechanisms of eukaryotic parasites and medically
important human pathogens such as free-living and enteric amoebic parasites.
Using a wide variety of methods, we particularly focus on the quantitative
identification of proteins from cellular compartments (proteomics)
and perform fundamental research on novel anti-infectives.
• Ancient weapons – cytolytic and antimicrobial polypeptides as defence effector molecules of animals
Antimicrobial systems in animals have been characterized at the molecular level primarily for vertebrates and arthropods. A variety of active peptides have been found and they possess highly diverse structures. The majority of them share the common feature of amphipathicity and appear to act by physical disruption of the membranes of their targets. As the mode of action suggests that their application will not create resistant strains of pathogens, such peptides are currently used as natural templates to design new antibiotics.
Among the several groups of membrane-permeabilizing peptides classified so far, the one to which the subjects of our studies belong is extraordinary; its members are relatively large polypeptides and are characterized by a compact alpha-helical and disulfide-bonded fold. Such polypeptides can be found in species of amoeboid protozoa (e.g. amoebapores), organisms which may be viewed primarily as insatiable phagocytic cells that uses bacteria as a nutrient source, in invertebrates and in vertebrates. Porcine and human cytotoxic lymphocytes contain similar peptides, termed NK-lysin and granulysin, respectively, which appear to be an important constituents of the internal defence against pathogens, e.g. intracellular bacteria. We are comparing the structures of the various antimicrobial and/or cytotoxic polypeptides and monitor their biological activities to extract the similarities and differences of effector molecules from evolutionarily highly divergent animals.
We also are characterizing antimicrobial and cytolytic proteins from body fluids of invertebrate species, such as bacteria-degrading lysozymes or various cytolysins, some of which create electron microscopically visible ring-like lesions on target cell membranes reminiscent of bacterial pore-forming toxins and of the complement system of mammals. These proteins may be viewed as broad spectrum defensive weapons against prokaryotic and eukaryotic pathogens.
with the nematode Caenorhabditis elegans a multicellular model
organism has been introduced in our project. As the entire genome of the
worm has been elucidated and sophisticated techniques to manipulate the
organism have been established, it is possible to analyze the antimicrobial
system at the molecular and organismal level using DNA array technology
and functional knock-out mutants. We are focussing on the molecular basis
of the epithelial defense in C. elegans. Here, we are characterizing
the molecular mechanisms which combat infections of epithels that are
constantly exposed to potential pathogens, from target recognition to
signal transduction and eventually synthesis and secretion of effector
• Comparative and quantitative proteomics of microbe-challenged versus unchallenged Caenorhabditis elegans, an invertebrate model organism for innate immunity and inflammation
consensus view is that the intestinal epithelium of animals forms a physical
barrier to limit access of enteric microbes to the inner milieu of the
host and contributes to innate host defense by producing effector molecules,
e.g. antimicrobial peptides and enzymes, against particular luminal microbes.
Classical studies on processes involved in innate immunity, inflammation,
and pathology are often time-consuming, costly, and ethically problematic.
In recent years, invertebrate model organisms have been employed to get
out of this dilemma.
• Archaic cytolytic and antimicrobial mechanisms of free-living and pathogenic protozoa compared to those of higher eukaryotes
Many natural cytotoxic and antimicrobial proteins act by permeabilizing the target cell membranes. Presumably the most ancient phylogenetic location of such membrane-active polypeptides in eukaryotes has been found in amoebae. We found cytotoxic and antimicrobial polypeptides in enteric human pathogens (Entamoeba histolytica) and in free-living amoeboid protozoa (Naegleria, Acanthamoeba, Balamuthia) which are potentially highly pathogenic for humans. We are analyzing the structures of these amoebic proteins and determine their biological activities to elucidate the similarities and differences of these effector molecules. As an intensively studied and genetically tractable cellular model system, we are using the free-living and non-pathogenic amoeboid protozoon Dictyostelium discoideum to study the molecular armament which such a primitive phagocyte may use to combat growth of phagocytozed bacteria inside its digestive vacuoles.
figure: Entamoeba histolytica represented as a bacteria-phagocytozing
(at the left) and cytolytic effector cell (at the right). In both scenarios,
granule proteins such as the amoebapores are considered instrumental in
killing the target cell.
can transform from the amoebic phase upon streaming (1) into multicellular
aggregates that migrate and are termed slugs (2) which eventually will
become `fruiting bodies´ (3). These slugs contain specialized phagocytosing
cells that are proposed to fullfil functions comparable to those of immune
cells of higher organisms. Accordingly, slugs are valuable objects for