Are there chitosan receptors?
A few chitosan-binding proteins have been described from some plant species, and these have also been suggested to be involved in chitosan perception, but there is no experimental evidence for this claim. At least some, if not all chitosan-induced responses in the model plant Arabidopsis thaliana depend upon the presence of the chitin receptor, suggesting that this complex receptor might be responsible for chitosan perception in plants. While this is in line with the observation that the biological activity of chitosan oligomers increases with increasing degree of acetylation, it is less consistent with the fact that chitosan polymers of medium degree of acetylation appear to be more active elicitors in plants than those with higher degrees of acetylation. This, however, may also be related to the presence of chitinases in plants which might degrade these latter chitosan polymers more quickly to elicitor-inactive oligomers than the former ones. It has been suggested that in mammalian stem cells, an overexpressed receptor specific for hyaluronic acid called CD44, also recognizes chitosan.