Priority Research Area Infections

Biophysics

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Projects

The basic philosophy of the Laboratory Group Biophysics is the consistent interdisciplinary connection between biology, chemistry and physics. The focus is on biological questions with medical relevance in pulmonary infections. To answer these questions we have acquired and further developed various biophysical methods. The laboratory group deals with the structure and function of different membranes and their interaction with peptides and proteins. The bacterial membranes of lung-relevant germs have a special focus. The lipids from natural membranes are purified, characterized and then reconstituted in well-defined systems. Whole cells, natural membranes as well as reconstituted membranes are investigated with different biophysical methods (Figure 1).

Fig. 1: Scientific projects.

 

In addition to the methods available on site, regular measurements are carried out at various synchrotron sources in Germany and Europe.

 

The following questions are of central importance (Figure 2):

  1. characterisation of membrane structures
  2. activity of pore-forming antimicrobial peptides
  3. activity of microbial toxins
  4. microbial adhesion
  5. intracellular survival strategies
  6. distribution of bacteria by aerosols
  7. interaction of active substances in aerosols with membranes

Fig. 2: Biomedical Question

Reconstitution Systems
To mimic bacterial and immune cell membranes we established new reconstitution systems. The bilayers were composed of phospholipids, lipid II, and lysyl-PG to mimic the membrane of Gram-positive bacteria, and phospholipids and cholesterol to mimic the cytoplasmic membrane of eukaryotic cells. Furthermore, we reconstituted the outer membrane of Gram-negative bacteria as asymmetric planar lipid bilayer and also as asymmetric liposomes with one side composed of lipopolysaccharides (LPS), the other of phospholipids. In first attempts we have been successful to mimic the mycobacterial wax layer by using lipid matrices containing the glycolipid trehalose dimycolate (TDM).
 
Function of Antimicrobial Peptides (AMPs)
The AMPs we have investigated within the last years differ in their structure and activity. Starting with our hypothesis that lipid- and peptide-specific properties are responsible for the sensitivity or resistance of certain bacterial strains, we have characterized the interactions between the AMPs and reconstituted lipid membranes. For our investigations we have used various AMPs in their natural form as well as synthetic derivatives thereof. An almost perfect correlation between the biological activity of the AMPs investigated and their interaction with pure lipid matrices has been found. Thus, as a first step, the permeabilization of the lipid membrane is an essential prerequisite for bacterial killing. Based on our findings we were able to synthesize first generation peptides with improved activities. In addition to the pore formation we investigated further mechanisms including membrane fusion or aggregation induced by hydramacin and membrane encapsulation induced by the C-reactive protein from Limulus.
 
Development of new polypeptides as general microbiocides
We have developed new peptides, which were directed to combat against the Gram-negative sepsis in that the main pathogenicity factor LPS is neutralized by the peptides. Thus, these were called SALP (synthetic anti-LPS peptides). They were shown to effectively block the inflammation reaction in vitro as well as the systemic inflammation in vivo (mouse model of endotoxemia and of infection by bacteria) as well as to inhibit Gram-positive pneumonia in combination with an antibiotic. Additionally, some of the peptides were shown to considerably inhibit virus replication in human cells, such as those of the human immunodeficiency virus (HIV), Herpes simplex viruses I and II, hepatitis B, seasonal influenza H3N2, Dengue fever virus, and classical swine fever virus. The mechanisms of the anti-septic action and of virus replication differ: For the anti-septic activity, a direct binding to the bacterial pathogens take place, but also a binding to cell surface receptors such as CD14 and TLR4.
 
Survival strategies of intracellular pathogenes
If microbes are ingested by professional phagocytes, different interactions can happen in their phagosomes. These effects can lead to bacterial killing or even to survival of some intra-cellular microbes. There is evidence that on the one hand the phagocyte uses pore-forming peptides of the innate immunity, the so-called host defense peptides (HDP), to kill the microbes, and on the other hand microbes use pore-forming proteins and peptides, for example to prevent acidification of the phagosome. In addition to the elucidation of the underlying mechanisms of action, a central aim is to solve the question of how the microbes and the host protect themselves against the action of their own membrane-active substances. The outer membrane of mycobacteria contains the glycolipid trehalose dimycolate (TDM). The membrane-forming function of TDM and the interaction with different HDPs is characterized.