Bacteroidetes use thousands of enzyme combinations to break down glycans

• Published in: Nature communications 2019-05, Vol.10 (1), p.2043-2043, Article 2043
• Main Authors: Lapébie, Pascal, Lombard, Vincent, Drula, Elodie, Terrapon, Nicolas, Henrissat, Bernard
• Format: Article
• Language: English
• Subjects: 631/114/2785; 631/326/41/2530; 631/45/221; 631/45/72; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteroidetes; Bacteroidetes - genetics; Bacteroidetes - metabolism; Carbohydrates; Composition; Deoxyribonucleic acid; Depolymerization; DNA; Ecosystems; Enzymes; Enzymes - genetics; Enzymes - metabolism; Gene clusters; Genetic Loci; Genome, Bacterial - genetics; Genomes; Glycan; Humanities and Social Sciences; Isomerism; Isomers; Life Sciences; multidisciplinary; Polysaccharides; Polysaccharides - chemistry; Polysaccharides - metabolism; Saccharides; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-10068-5

Unlike proteins, glycan chains are not directly encoded by DNA, but by the specificity of the enzymes that assemble them. Theoretical calculations have proposed an astronomical number of possible isomers (> 10 12 hexasaccharides) but the actual diversity of glycan structures in nature is not known. Bacteria of the Bacteroidetes phylum are considered primary degraders of polysaccharides and they are found in all ecosystems investigated. In Bacteroidetes genomes, carbohydrate-degrading enzymes (CAZymes) are arranged in gene clusters termed polysaccharide utilization loci (PULs). The depolymerization of a given complex glycan by Bacteroidetes PULs requires bespoke enzymes; conversely, the enzyme composition in PULs can provide information on the structure of the targeted glycans. Here we group the 13,537 PULs encoded by 964 Bacteroidetes genomes according to their CAZyme composition. We find that collectively Bacteroidetes have elaborated a few thousand enzyme combinations for glycan breakdown, suggesting a global estimate of diversity of glycan structures much smaller than the theoretical one. Bacteroidetes genomes contain polysaccharide utilization loci (PULs), each of which encodes enzymes for the breakdown of one particular glycan. By analyzing the enzyme composition of 13,537 PULs, the authors suggest that the natural glycan diversity is orders of magnitude lower than previously proposed.