The
research group of Prof. Dr. Bruno Moerschbacher has twenty years of
experience in research on biologically active polysaccharides from
plant and fungal cell walls. Lately, the main focus of the research has
been on structure/function-relationships of partially acetylated
chitosans. We are interested in elucidating the roles of the degree of
polymerisation (DP), the degree of acetylation (DA), and the pattern of
acetylation (PA) of chitosan oligomers and polymers on their
biological
activities towards micro-organisms as well as plant and human cells. We
found the
antibacterial and antifungal activities to be mainly
determined by the DA of chitosan polymers, while the
plant disease
resistance inducing activities of chitosan polymers and oligomers were
strongly influenced by both DA and DP. In collaboration with the group
of Prof. Schneider from the Department of Dermatology, we found that
the biological activities towards different types of human cells, e.g.
pro-inflammatory activities towards macrophages, are more complex and
we have postulated that in addition to DA and DP, the PA, i.e. the
distribution of acetyl groups along the linear chitosan chain,
crucially influences these activities. However, all chitosans available
today are produced from fully acetylated chitin using chemical methods
of partial de-acetylation or complete de-acetylation followed by
partial re-acetylation - and these methods invariably yield chitosans
with random PA. We have therefore started to develop enzymatic tools
for the generation and analysis of chitosan oligomers and polymers with
non-random PA. We are using metagenomic as well as knowledge-based
approaches to identify novel
chitosan modifying enzymes, such as chitin
de-acetylases and sequence-specific chitosan hydrolases, we clone and
express their genes heterologously either in
E. coli or in the
fission yeast
S. pombe, and we analyse the purified enzymes concerning
e.g. their substrate specificities, cleavage mechanisms, and product
patterns. We will now use
protein engineering to optimise these enzymes
for the generation and characterisation of chitosans with non-random PA
which we can then analyse for their biological activities. Based on the
knowledge gained, we are developing, together with Industry, improved
chitosan-based
plant disease protectants and
wound dressings. Our work
is supported by a strong interdisciplinary and international network
with physico-chemists, pharmacological engineers, and medical
physiologists in Europe and world-wide, from both Academia and Industry.
expertise offered:- gene isolation and identification, cloning and heterologous expression (E. coli, S. pombe, A. thaliana)
- enzyme isolation and identification, purification and characterisation (chitin/chitosan and pectin/pectate modifying enzymes, polyphenoloxidases)
- mono-, oligo-, and polysaccharide analysis (GLC, HPAEC-PED)
- enzymatic fingerprinting to analyse pattern of chitosan acetylation
- HF-solvolysis at controlled low temperature
- bioactivity assays (anti-bacterial, anti-fungal, plant resistance inducing activities)
- generation and analysis of transgenic plants (A. thaliana, T. officinale, overexpression, RNAi)
- axenic culture of the obligately biotrophic wheat stem rust fungus (P. graminis f.sp. tritici)
