OB-24:

Uptake of a chitin-degradation product via the constitutive N-acetylglucosamine/N,N’-diacetylchitobiose binding protein NgcE^SCO of an ABC transporter in Streptomyces coelicolor A3(2)

Streptomyces coelicolor A3(2) is supposed to possess plural ABC transporters for uptake of the chitin-degradation product N,N-diacetylchitobiose [(GlcNAc)₂]. One is the DasABC-MsiK system and another is the NgcEFG-MsiK. We report here biochemical and genetic characterization of NgcE^SCO, which shares 34% identical amino acid sequence with NgcE of the previously characterized N-acetylglucosamine (GlcNAc)/(GlcNAc)₂-ABC transporter Ngc in S. olivaceoviridis. The recombinant NgcE^SCO protein produced in Escherichia coli interacted with GlcNAc and (GlcNAc)₂, and its Kd values (1.15 and 1.53 microM, respectively) for those sugars were relatively high as a solute-binding protein of ABC transporter. Immuno-blot and reverse-transcription PCR analyses demonstrated that the ngcE^SCO gene was rather constitutively expressed, in contrast to the dasA gene that is inducible by (GlcNAc)₂. The disruption of the ngcE^SCO gene rarely affected the (GlcNAc)₂ consumption, while the (GlcNAc)₂ consumption rate was significantly reduced in the dasA null mutant. The ngcE^SCO-dasA double mutant consumed (GlcNAc)₂ more slowly than the dasA mutant. NgcE^SCO is thus revealed to be a constitutive and low affinity GlcNAc/(GlcNAc)₂-binding protein for (GlcNAc)₂-uptake in S. coelicolor A3(2). Induction of chitinase production by (GlcNAc)₂ was abolished in the ngcE^SCO-dasA double mutant although it was not affected in the ngcE^SCO mutant. By contrast, in the presence of colloidal chitin, chitinase production was delayed in the ngcE^SCO mutant. The ngcE^SCO gene might be involved in the initial response for chitin recognition in S. coelicolor A3(2).

keywords:transporter,chitin,actinomycetes