Enzymatic and genetic characterization of the DasD protein possessing N-acetyl-[beta]-d-glucosaminidase activity in Streptomyces coelicolorA3(2)

The dasD gene is located just downstream of the dasABC gene cluster, encoding components of an ABC transporter for uptake of a chitin-degradation product N,N'-diacetylchitobiose [(GlcNAc)2] in Streptomyces coelicolorA3(2). To clarify the roles of the DasD protein in the degradation and assimilation of chitin, we obtained and characterized a recombinant DasD protein and a dasD-null mutant of S. coelicolorA3(2). The recombinant DasD protein produced in Escherichia coli showed N-acetyl-[beta]-d-glucosaminidase (GlcNAcase) activity and its optimum temperature and pH were 40 °C and 7, respectively. dasD transcription was strongly induced in the presence of chitin, weakly by chitosan, but not by cellulose or xylan in S. coelicolorA3(2). Immuno-blot analysis demonstrated that DasD is a cytoplasmic protein. The dasD-null mutant exhibited cellular GlcNAcase activity which was comparable with that of the parent strain M145. DasD, thus, did not seem to be a major GlcNAcase. Induced extracellular chitinase activity in the dasD-null mutant was, interestingly, higher than M145, in the presence of colloidal chitin or (GlcNAc)2. In contrast to M145, (GlcNAc)2 temporally accumulated in the culture supernatant of the dasD-null mutant in the presence of colloidal chitin. [PUBLICATION ABSTRACT]