Multi-proteomics reveals integrated metabolic and regulatory networks for xylan catabolism in Streptomyces sp. SirexAA-E.

An insect-associated bacterium, Streptomyces sp. SirexAA-E (SirexAA-E) secretes plant biomass-degrading enzymes depending on the available cell wall materials. SirexAA-E readily utilizes xylan, one of the major hemicelluloses. However, the enzyme composition and pathways supporting xylan metabolism in SirexAA-E and other Streptomycetes have not been reported. We aimed to understand changes in both extracellular and intracellular protein productions by cultivating SirexAA-E in defined media containing either xylose, xylobiose, or xylan. Proteomics showed each carbon source gave specific extracellular protein composition when compared to glucose. Furthermore, intracellular proteomics using a pair-wise Tandem Mass Tag (TMT)-labeling LC-MS/MS identified 1,037 proteins with changes in the xylose-, xylobiose-, or xylan-dependent proteome relative to the glucose-derived proteome. We found that numerous proteins related to oxidative phosphorylation were enriched in the pentose-grown proteomes relative to the glucose proteome. This observation is consistent with a high demand for ATP to support protein secretion and intake of xylose and xylooligosaccharides. Additionally, several transporters for carbon uptake were identified in the genome of SirexAA-E by protein homology comparison with Streptomyces coelicolor, and several key transcriptional regulators used by SirexAA-E for catabolizing xylan were found by pull-down proteomics. The current study provides new insights into the extensive extracellular and intracellular responses of a cellulolytic Streptomyces to the major plant hemicellulose.IMPORTANCEStreptomyces sp. SirexAA-E can efficiently degrade cellulose, xylan, and mannan, the major polysaccharide components of woody biomass. Our previous work showed the relative simplicity of the secreted proteome used to degrade cellulose. In this study, we report on the extracellular and intracellular proteomic responses of SirexAA-E during growth on xylan. The substrate-specific proteomic profiles have given a new understanding of the regulation of xylanolytic enzymes and additional metabolic pathways supporting growth on a pentose sugar. These groupings of regulatory and structural proteins provide a blueprint for construction of more robust strains for biomass valorization.