title: A cellulase/xylanase-negative mutant of Streptomyces lividans 1326 defective in cellobiose and xylobiose uptake is mutated in a gene encoding a protein homologous to ATP-binding proteins.
abstract: The uptake of monosaccharides (glucose and xylose) and disaccharides (cellobiose and xylobiose) was evaluated in the Streptomyces lividans mutant strain 10-164. The pleiotropic mutation had no effect on glucose uptake; however, the Vmax of xylose uptake was decreased 10-fold as compared to the wild-type strain, S. lividans 1326, and the transport system of cellobiose and xylobiose, the putative inducers of the cellulase and xylanase genes, was completely abolished resulting in a cellulase/xylanase-negative mutant. An accumulation of xylose and glucose in culture media was observed when the mutant was grown on xylobiose and cellobiose, respectively. Cell-associated beta-glucosidase and low levels of extracellular beta-glucosidase were detected in both strains. When gluconolactone, a beta-glucosidase inhibitor, was added to the medium there was no uptake of cellobiose or release of glucose by the mutant strain, whereas the uptake of cellobiose by the wild-type strain was not significantly affected. It is thus proposed that the active transport system for cellobiose and xylobiose is affected in mutant strain 10-164. Glucose and xylose production from disaccharide hydrolysis are due to beta-glucosidase and beta-xylosidase activities, which sustain the growth of the mutant strain. Clones complementing the mutation were isolated from a gene bank constructed using mutant strain 10-164. The msiK gene codes for MsiK, a 40 kDa multiple sugar import protein, which belongs to the family of ATP-binding proteins. The mutation is located in the B site which is responsible for ATP binding. This protein probably provides energy to the xylose and disaccharide transport system as a result of the hydrolysis of ATP.
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics*; D000255:Adenosine Triphosphate; D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics; D002475:Cellobiose / Q000378:metabolism*; D002480:Cellulase / Q000235:genetics; D003001:Cloning, Molecular; D004187:Disaccharides / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005798:Genes, Bacterial / Q000235:genetics*; D005942:Gluconates / Q000494:pharmacology; D007700:Kinetics; D007783:Lactones; D008969:Molecular Sequence Data; D009154:Mutation; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013302:Streptomyces / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D043325:Xylan Endo-1,3-beta-Xylosidase; D014994:Xylose / Q000378:metabolism; D014995:Xylosidases / Q000235:genetics; D001617:beta-Glucosidase / Q000037:antagonists & inhibitors
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D004187:Disaccharides; D004791:Enzyme Inhibitors; D005942:Gluconates; D007783:Lactones; D002475:Cellobiose; D000255:Adenosine Triphosphate; D014994:Xylose; D014995:Xylosidases; D001617:beta-Glucosidase; D043325:Xylan Endo-1,3-beta-Xylosidase; D002480:Cellulase; D000251:Adenosine Triphosphatases; C096958:MsiK protein, Streptomyces; C004173:xylobiose; C010730:beta-glucono-1,5-lactone