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Partial redundancy in the synthesis of the D-arabinose incorporated in the cell wall arabinan of Corynebacterineae

Bénoit Van-der-Rest^1,

¹ Université Toulouse III (Université Paul Sabatier) et Centre National de la Recherche Scientifique (CNRS), Institut de Pharmacologie et Biologie Structurale (UMR 5089), Département "Mécanismes Moléculaires des Infections Mycobactériennes", 205 route de Narbonne, F-31077 Toulouse cedex 04, France
² Institut de Génétique et Microbiologie, Université Paris-Sud, F-91405 Orsay, France
³ Centre National de la Recherche Scientifique, F-91405 Orsay, France
⁴ Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, CO 80523-1682, USA

Correspondence
Christine Houssin
christine.houssin{at}igmors.u-psud.fr

The major cell wall carbohydrate of Corynebacterineae is arabinogalactan (AG), a branched polysaccharide that is essential for the physiology of these bacteria. Decaprenylphosphoryl-D-arabinose (DPA), the lipid donor of D-arabinofuranosyl residues of AG, is synthesized through a series of unique biosynthetic steps, the last one being the epimerization of decaprenylphosphoryl-β-D-ribose (DPR) into DPA, which is believed to proceed via a sequential oxidation–reduction mechanism. Two proteins from Mycobacterium tuberculosis (Rv3790 and Rv3791) have been shown to catalyse this epimerization in an in vitro system. The present study addressed the exact function of these proteins through the inactivation of the corresponding orthologues in Corynebacterium glutamicum (NCgl0187 and NCgl0186, respectively) and the analysis of their in vivo effects on AG biosynthesis. We showed that NCgl0187 is essential, whereas NCgl0186 is not. Deletion of NCgl0186 led to a mutant possessing an AG that contained half the arabinose and rhamnose, and less corynomycolates linked to AG but more trehalose mycolates, compared with the parental strain. A candidate gene that may encode a protein functionally similar to NCgl0186 was identified in both C. glutamicum (NCgl1429) and M. tuberculosis (Rv2073c). While the deletion of NCgl1429 had no effect on AG biosynthesis of the mutant, the gene could complement the mycolate defect of the AG of the NCgl0186 mutant, strongly supporting the concept that the two proteins play a similar function in vivo. Consistent with this, the NCgl1429 gene appeared to be essential in the NCgl0186-inactivated mutant. A detailed bioinformatics analysis showed that NCgl1429, NCgl0186, Rv3791 and Rv2073c could constitute, with 52 other proteins belonging to the actinomycetales, a group of closely related short-chain reductases/dehydrogenases (SDRs) with atypical motifs. We propose that the epimerization of DPR to DPA involves three enzymes that catalyse two distinct steps, each being essential for the viability of the bacterial cells.

Present address: École Nationale Supérieure Agronomique de Toulouse, Avenue de l'Agrobiopole, BP 32607 Auzeville-Tolosane, F-31326 Castanet-Tolosan cedex, France.

Two supplementary tables, listing the primers used in this study and the orthologous group of proteins obtained by computational analysis using protein sequence alignments of strains examined in this study, are available with the online version of this paper.