title: Decaprenylphosphoryl arabinofuranose, the donor of the D-arabinofuranosyl residues of mycobacterial arabinan, is formed via a two-step epimerization of decaprenylphosphoryl ribose.
abstract: The major cell wall polysaccharide of mycobacteria is a branched-chain arabinogalactan in which arabinan chains are attached to the 5 carbon of some of the 6-linked galactofuranose residues; these arabinan chains are composed exclusively of D-arabinofuranose (Araf) residues. The immediate precursor of the polymerized Araf is decaprenylphosphoryl-D-Araf, which is derived from 5-phosphoribose 1-diphosphate (pRpp) in an undefined manner. On the basis of time course, feedback, and chemical reduction experiment results we propose that decaprenylphosphoryl-Araf is synthesized by the following sequence of events. (i) pRpp is transferred to a decaprenyl-phosphate molecule to form decaprenylphosphoryl-beta-D-5-phosphoribose. (ii) Decaprenylphosphoryl-beta-D-5-phosphoribose is dephosphorylated to form decaprenylphosphoryl-beta-D-ribose. (iii) The hydroxyl group at the 2 position of the ribose is oxidized and is likely to form decaprenylphosphoryl-2-keto-beta-D-erythro-pentofuranose. (iv) Decaprenylphosphoryl-2-keto-beta-D-erythro-pentofuranose is reduced to form decaprenylphosphoryl-beta-D-Araf. Thus, the epimerization of the ribosyl to an arabinosyl residue occurs at the lipid-linked level; this is the first report of an epimerase that utilizes a lipid-linked sugar as a substrate. On the basis of similarity to proteins implicated in the arabinosylation of the Azorhizobium caulidans nodulation factor, two genes were cloned from the Mycobacterium tuberculosis genome and expressed in a heterologous host, and the protein was purified. Together, these proteins (Rv3790 and Rv3791) are able to catalyze the epimerization, although neither protein individually is sufficient to support the activity.
authors.affiliation: Department of Biochemistry, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia.
authors.forename: Katarína
authors.initials: K
authors.lastname: Mikusová
authors.forename: Hairong
authors.initials: H
authors.lastname: Huang
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Yagi
authors.forename: Marcelle
authors.initials: M
authors.lastname: Holsters
authors.forename: Danny
authors.initials: D
authors.lastname: Vereecke
authors.forename: Wim
authors.initials: W
authors.lastname: D'Haeze
authors.forename: Michael S
authors.initials: MS
authors.lastname: Scherman
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Brennan
authors.forename: Michael R
authors.initials: MR
authors.lastname: McNeil
authors.forename: Dean C
authors.initials: DC
authors.lastname: Crick
mesh_terms: D001089:Arabinose / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002238:Carbohydrate Epimerases / Q000235:genetics / Q000378:metabolism; D011756:Diphosphates / Q000737:chemistry / Q000378:metabolism; D020102:Mycobacterium smegmatis / Q000201:enzymology / Q000378:metabolism*; D011106:Polyisoprenyl Phosphates / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012266:Ribose / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D011756:Diphosphates; D011106:Polyisoprenyl Phosphates; D011134:Polysaccharides; D011994:Recombinant Proteins; C431714:arabinofuranose; C030080:araban; C068697:decaprenyl phosphate; D012266:Ribose; D001089:Arabinose; D002238:Carbohydrate Epimerases