Characterization of the binding protein-dependent cellobiose and cellotriose transport system of the cellulose degrader Streptomyces reticuli

Streptomyces reticuli has an inducible ATP-dependent uptake system specific for cellobiose and cellotriose. By reversed genetics a gene cluster encodi ng components of a binding protein-dependent cellobiose and cellotriose ABC transporter was cloned and sequenced. The deduced gene products comprise a regulatory protein (CebR), a cellobiose binding lipoprotein (CebE), two in tegral membrane proteins (CebF and CebG), and the NH2-terminal part of an i ntracellular P-glucosidase (BglC), The gene for the ATP binding protein Msi K is not linked to the ceb operon, We have shown earlier that MsiK is part of two different ABC transport systems, one for maltose and one for cellobi ose and cellotriose, in S. reticuli and Streptomyces lividans. Transcriptio n of polycistronic: cebEFG and bglC mRNAs. is induced by cellobiose, wherea s the cebR gene is transcribed independently. Immunological experiments sho wed that CebE is synthesized during growth crith cellobiose and that MsiK i s produced in the presence of several sugars at high, or moderate levels. T he described ABC transporter is the first one of its kind and is the only s pecific cellobiose/cellotriose uptake system of S. reticuli, since insertio nal inactivation of the cebE gene prevents high-affinity uptake of cellobio se.