title: DipA, a pore-forming protein in the outer membrane of Lyme disease spirochetes exhibits specificity for the permeation of dicarboxylates.
abstract: Lyme disease Borreliae are highly dependent on the uptake of nutrients provided by their hosts. Our study describes the identification of a 36 kDa protein that functions as putative dicarboxylate-specific porin in the outer membrane of Lyme disease Borrelia. The protein was purified by hydroxyapatite chromatography from Borrelia burgdorferi B31 and designated as DipA, for dicarboxylate-specific porin A. DipA was partially sequenced, and corresponding genes were identified in the genomes of B. burgdorferi B31, Borrelia garinii PBi and Borrelia afzelii PKo. DipA exhibits high homology to the Oms38 porins of relapsing fever Borreliae. B. burgdorferi DipA was characterized using the black lipid bilayer assay. The protein has a single-channel conductance of 50 pS in 1 M KCl, is slightly selective for anions with a permeability ratio for cations over anions of 0.57 in KCl and is not voltage-dependent. The channel could be partly blocked by different di- and tricarboxylic anions. Particular high stability constants up to about 28,000 l/mol (in 0.1 M KCl) were obtained among the 11 tested anions for oxaloacetate, 2-oxoglutarate and citrate. The results imply that DipA forms a porin specific for dicarboxylates which may play an important role for the uptake of specific nutrients in different Borrelia species.
authors.affiliation: Rudolf-Virchow-Center, DFG-Research Center for Experimental Biomedicine, University of Würzburg, Würzburg, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Thein
authors.forename: Mari
authors.initials: M
authors.lastname: Bonde
authors.forename: Ignas
authors.initials: I
authors.lastname: Bunikis
authors.forename: Katrin
authors.initials: K
authors.lastname: Denker
authors.forename: Albert
authors.initials: A
authors.lastname: Sickmann
authors.forename: Sven
authors.initials: S
authors.lastname: Bergström
authors.forename: Roland
authors.initials: R
authors.lastname: Benz
mesh_terms: D000818:Animals; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism; D001898:Borrelia / Q000235:genetics / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000502:physiology*; D029382:Dicarboxylic Acid Transporters / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008193:Lyme Disease / Q000235:genetics / Q000378:metabolism; D011817:Rabbits; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029382:Dicarboxylic Acid Transporters