In our research we use a wide variety of biopolymer systems, each of which has certain advantages and drawbacks. The main reason for using particle of biological origin is that Nature is capable of assembling structure of unmatched complexity and reproducibility. Studying these assemblages enables us to uncover novel phenomena that is not easily observe in conventional chemically systems.
Filamentous viruses (fd, M13)
When compared to most rods grown via chemical synthesis, the filamentous viruses have a very high degree of monodispersity, i. e. all the viruses have the same length. For this reason, using filamentous viruses we have been able to observe a whole range of phenomena that is usually not observed in comparable synthetic systems. Furthermore, over the past few years we have begun to systematically mutate the virus DNA in order to vary its contour length, flexibility and chirality. This gives us control over all important microscopic parameters and enables to establish a firm experimental connection between microscopic parameters and macroscopic behavior.
Bacterium spins filaments with helical shape (bacterial flagella) at very high speed in order to propel itself forward. The unique feature of flagellum is its polymorphic transitions between states with widely different helicity. The entire flagellum switches between two states in responds to a variety of external stimuli (pH, ionic strength, temperature ...). Bacterial flagella are a unique system that allows to investigate how filament helicity influences their assembly and macroscopic behavior.
F-Actin is a biologically important filament that assembles from monomeric protein G-actin. It is a semiflexible polymer with a persistence length of 16 microns. If purified correctly the contour length of actin filaments can be larger then 100 microns. Its large size and persistence length make actin filaments ideally suited for direct visualization and manipulation with optical microscopy. Although most actin filaments are linear, recently we have also been able to define conditions which greatly enhance the assembly of actin filaments with ring conformation. Moreover we have shown that certain fluorescent labels induce actin filaments to switch between multiple conformation.
We have recently started working on microtubules, which are very stiff filaments assembled from monomeric tubulin proteins. These filaments play an important role in a variety of cellular processes.