Structural highlights
Publication Abstract from PubMedStreptomyces sp. SirexAA-E is a highly cellulolytic bacterium isolated from an insect/microbe symbiotic community. When grown on lignin-containing biomass, it secretes SACTE_2871, an aromatic ring dioxygenase domain fused to a family 5/12 carbohydrate-binding module (CBM 5/12). Here we present structural and catalytic studies of this novel fusion enzyme, thus providing insight into its function. The dioxygenase domain has the core beta sandwich fold typical of this enzyme family but lacks a dimerization domain observed in other intradiol dioxygenases. Consequently, the X-ray structure shows that the enzyme is monomeric and the Fe(III)-containing active site is exposed to solvent in a shallow depression on a planar surface. Purified SACTE_2871 catalyzes the O2-dependent intradiol cleavage of catecholic compounds from lignin biosynthetic pathways, but not their methoxylated derivatives. Binding studies show that SACTE_2871 binds synthetic lignin polymers and chitin through the interactions of the CBM 5/12 domain, representing a new binding specificity for this fold family. Based on its unique structural features and functional properties, we propose that SACTE_2871 contributes to the invasive nature of the insect/microbial community by destroying precursors needed by the plant for de novo lignin biosynthesis as part of its natural wounding response. Fusion of dioxygenase and lignin-binding domains in a novel secreted enzyme from cellulolytic Streptomyces sp. SirexAA-E.,Bianchetti CM, Harmann CH, Takasuka TE, Hura GL, Dyer K, Fox BG J Biol Chem. 2013 May 7. PMID:23653358[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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