Uptake of a chitin-degradation product via the constitutive N-acetylglucosamine/N,N’-diacetylchitobiose binding protein NgcESCO of an ABC transporter in Streptomyces coelicolor A3(2)
1Graduate School of Advanced Integration Science, Chiba Univ., 2Department of Advanced Bioscience, Kinki Univ., 3School of Agriculture, Meiji Univ., 4Shizuoka Institute of Science and Technology, 5National Institute of Agro-Environmental Sciences
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 NgcESCO, 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 NgcESCO 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 ngcESCO gene was rather constitutively expressed, in contrast to the dasA gene that is inducible by (GlcNAc)2. The disruption of the ngcESCO gene rarely affected the (GlcNAc)2 consumption, while the (GlcNAc)2 consumption rate was significantly reduced in the dasA null mutant. The ngcESCO-dasA double mutant consumed (GlcNAc)2 more slowly than the dasA mutant. NgcESCO 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 ngcESCO-dasA double mutant although it was not affected in the ngcESCO mutant. By contrast, in the presence of colloidal chitin, chitinase production was delayed in the ngcESCO mutant. The ngcESCO gene might be involved in the initial response for chitin recognition in S. coelicolor A3(2).