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

Author

Meniche, Xavier, de Sousa-d'Auria, Celia, Van-der-Rest, Benoit, Bhamidi, Suresh, Huc, Emilie, Huang, Hairong, De Paepe, Diane, Tropis, Marielle, McNeil, Mike, Daffe, Mamadou, and Houssin, Christine

Subjects
Bacterial cell walls -- Physiological aspects, Peptidoglycans -- Physiological aspects, Peptidoglycans -- Research, Polysaccharides -- Physiological aspects, Polysaccharides -- Research, Biological sciences
Abstract

The major cell wall carbohydrate of Corynebacterineae is arabinogalactan (AG), a branched polysaccharide that is essential for the physiology of these bacteria. Decaprenylphosphoryl-Darabinose (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-[beta]-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 (NCg10187 and NCg10186, respectively) and the analysis of their in vivo effects on AG biosynthesis. We showed that NCg10187 is essential, whereas NCg10186 is not. Deletion of NCgI0186 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 (NCgI1429) and M. tuberculosis (Rv2073c). While the deletion of NCgI1429 had no effect on AG biosynthesis of the mutant, the gene could complement the mycolate defect of the AG of the NCgI0186 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 NCglO186-inactivated mutant. A detailed bioinformatics analysis showed that NCgI1429, NCg10186, 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.

Published
2008

6. The Plant Short-Chain Dehydrogenase (SDR) superfamily: genome-wide inventory and diversification patterns

Author

Moummou, Hanane, Kallberg, Yvonne, Brice Tonfack, Libert, Persson, Bengt, van der Rest, Benoit, Moummou, Hanane, Kallberg, Yvonne, Brice Tonfack, Libert, Persson, Bengt, and van der Rest, Benoit

Abstract

Background: Short-chain dehydrogenases/reductases (SDRs) form one of the largest and oldest NAD(P)(H) dependent oxidoreductase families. Despite a conserved Rossmann-fold structure, members of the SDR superfamily exhibit low sequence similarities, which constituted a bottleneck in terms of identification. Recent classification methods, relying on hidden-Markov models (HMMs), improved identification and enabled the construction of a nomenclature. However, functional annotations of plant SDRs remain scarce. less thanbrgreater than less thanbrgreater thanResults: Wide-scale analyses were performed on ten plant genomes. The combination of hidden Markov model (HMM) based analyses and similarity searches led to the construction of an exhaustive inventory of plant SDR. With 68 to 315 members found in each analysed genome, the inventory confirmed the over-representation of SDRs in plants compared to animals, fungi and prokaryotes. The plant SDRs were first classified into three major types - classical, extended and divergent - but a minority (10% of the predicted SDRs) could not be classified into these general types (unknown or atypical types). In a second step, we could categorize the vast majority of land plant SDRs into a set of 49 families. Out of these 49 families, 35 appeared early during evolution since they are commonly found through all the Green Lineage. Yet, some SDR families - tropinone reductase-like proteins (SDR65C), ABA2-like-NAD dehydrogenase (SDR110C), salutaridine/menthone-reductase-like proteins (SDR114C), dihydroflavonol 4-reductase-like proteins (SDR108E) and isoflavone-reductase-like (SDR460A) proteins - have undergone significant functional diversification within vascular plants since they diverged from Bryophytes. Interestingly, these diversified families are either involved in the secondary metabolism routes (terpenoids, alkaloids, phenolics) or participate in developmental processes (hormone biosynthesis or catabolism, flower development), in opp, Funding Agencies|EGIDE|MA-06-155|Libert Brice Tonfack from "Service de Cooperation et dAction Culturelle" of the French Embassy (Cameroon)

Published
2012
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