title: The Rhizobium meliloti exoK gene and prsD/prsE/exsH genes are components of independent degradative pathways which contribute to production of low-molecular-weight succinoglycan.
abstract: When grown on medium supplemented with the succinoglycan-binding dye, Calcofluor, and visualized under UV light, colonies of Rhizobium meliloti (Sinorhizobium meliloti) exoK mutants produce a fluorescent halo with a delayed onset relative to wild-type colonies. By conducting transposon mutagenesis of exoK mutants of R. meliloti and screening for colonies with even more severe delays in production of these fluorescent halos, we identified three genes, designated prsD, prsE, and exsH, which are required for the eventual production of fluorescent halos by exoK colonies. Nucleotide sequence indicates that the prsD and prsE genes encode homologues of ABC transporters and membrane fusion proteins of Type I secretion systems, respectively, whereas exsH encodes a homologue of endo-1,3-1,4-beta-glycanases with glycine-rich nonameric repeats typical of proteins secreted by Type I secretion systems. The exoK gene and the prsD/prsE/exsH genes were shown to be components of independent pathways for production of extracellular succinoglycan degrading activities and for production of low-molecular-weight succinoglycan by R. meliloti. Based on these results, we propose that ExsH is a succinoglycan depolymerase secreted by a Type I secretion system composed of PrsD and PrsE, and that the ExsH and ExoK glycanases contribute to production of low-molecular-weight succinoglycan.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA.
authors.forename: G M
authors.initials: GM
authors.lastname: York
authors.forename: G C
authors.initials: GC
authors.lastname: Walker
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001557:Benzenesulfonates / Q000494:pharmacology; D005816:Genetic Complementation Test; D006026:Glycoside Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009154:Mutation; D016366:Open Reading Frames; D010641:Phenotype; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D016962:Sinorhizobium meliloti / Q000235:genetics* / Q000378:metabolism; D013559:Symbiosis
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D001557:Benzenesulfonates; D011135:Polysaccharides, Bacterial; C106236:PrsD protein, Rhizobium leguminosarum; C106237:PrsE protein, Rhizobium leguminosarum; C056779:succinoglycan; C007061:C.I. Fluorescent Brightening Agent 28; C112238:EXSH protein, Rhizobium meliloti; C112237:ExoK glycanase, Rhizobium meliloti; D006026:Glycoside Hydrolases; C020668:glycanase