Decaprenylphosphoryl arabinofuranose, the donor of the D-arabinofuranosyl residues of mycobacterial arabinan, is formed via a two-step epimerization of decaprenylphosphoryl ribose.
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.
Mikusová
Katarína
K
Department of Biochemistry, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia.
Huang
Hairong
H
Yagi
Tetsuya
T
Holsters
Marcelle
M
Vereecke
Danny
D
D'Haeze
Wim
W
Scherman
Michael S
MS
Brennan
Patrick J
PJ
McNeil
Michael R
MR
Crick
Dean C
DC
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*
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