Chitin, Chitinases and Chitinase-Like Proteins: A Hypothesis on Ancestral Relationships

In this contribution we reconsider the phylogeny of mammalian proteins homologous to the glycosyl hydrolase 18 family: chitinases and chitinase-like proteins. This problem has been recently dealt with in two important papers (Bussink et al, 2007; Funkhouser and Aronson, 2007). A clear scheme emerges from these analyses, in which chitinase-like proteins are specialized, tissue-specific, mammalian proteins that have lost the chitinolytic function and have acquired a wealth of possible new functions, mainly related to inflammatory processes. We present here preliminary results from different methods of sequence analysis based on: i) multiple alignments; ii) compression algorithms; iii) statistical over(under)-representation of short k-grams. From our preliminary exploration we formulate and discuss the hypothesis that, chitinase-like proteins are the ancestor group, present as pre-chitinase activators in an ancestral unicellular world from which active chitinases originated as a response to the emergence of chitin synthesis. Chitinase-like proteins in mammals could play a role, in inflammation and in cancer development, similar to the ancient role of activator or signalling molecules in unicellular organisms.