| Research Abstract |
Chitin, beta- (1,4) polymer of N-acetylglucosamine (GlcNAc), is a major costituent of the cell wall of fungi and the exoskelton of insects and crustaceans. This polymer is second only to cellulose in natural abundance and the annual production is estimated to be approximately 10^9-10^<11> tons. Thus, chitin has attracted the attention of many researchers as a reusable biomass.
The purpose of the present investigation is to clarify the chitin-degradation system in a molecular level in a marine bacterium, Alteromonas sp.strain O-7. Recently, it was found that this strain produced five kinds of chitinases (ChiA,B,C,D,E) was three kinds of N-acetylglucosaminidases (GlcNAcaseA,B,C) when the microorganism was grown in a medium containing chitin as a carbon source. Among them, the nucleotide sequences of ChiA,ChiC,GlcNacaseB and GlcNAcaseC genes were determined. Analysis and comparison of the deduced amino acid sequences revealed that ChiA and ChiC were composed of three domain structures. ChiA contained chitin-binding domain at its N-terminus, followed by a glycosyl hydrase family 18 catalytic domain and novel chitin and cellulose-binding domain (CBD). ChiC contained CBD at its N-terminus, followed by fibronectin type-II domain and catalytic domain.
We identified two acid residues (Glu and Asp) involved in the catalysis of ChiA.In the case of GlcNAcaseB,like chitinase, Asp-316 and Asp-348 seemed to be essential residues in the active site of the enzyme.
At the present time, we are cloning and sequencing the remaining chitinases and GlcNAcaseA genes to clarify the relationship between structure and function, and also studying the real inducer involved in the induction of chitin-degrading enzymes.
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