Structural highlights
Publication Abstract from PubMedClostridium thermocellum is actively being developed as a microbial platform to produce biofuels and chemicals from renewable plant biomass. An attractive feature of this bacterium is its ability to efficiently degrade lignocellulose using surface-displayed cellulosomes, large multi-protein complexes that house different types of cellulase enzymes. Clostridium thermocellum tailors the enzyme composition of its cellulosome using nine membrane-embedded anti-sigma factors (RsgI1-9), which are thought to sense different types of extracellular carbohydrates and then elicit distinct gene expression programs via cytoplasmic sigma factors. Here we show that the RsgI9 anti-sigma factor interacts with cellulose via a C-terminal bi-domain unit. A 2.0 A crystal structure reveals that the unit is constructed from S1C peptidase and NTF2-like protein domains that contain a potential binding site for cellulose. Small-angle X-ray scattering experiments of the intact ectodomain indicate that it adopts a bi-lobed, elongated conformation. In the structure, a conserved RsgI extracellular (CRE) domain is connected to the bi-domain via a proline-rich linker, which is expected to project the carbohydrate-binding unit ~160 A from the cell surface. The CRE and proline-rich elements are conserved in several other C. thermocellum anti-sigma factors, suggesting that they will also form extended structures that sense carbohydrates. The structure of the Clostridium thermocellum RsgI9 ectodomain provides insight into the mechanism of biomass sensing.,Mahoney BJ, Takayesu A, Zhou A, Cascio D, Clubb RT Proteins. 2022 Feb 23. doi: 10.1002/prot.26326. PMID:35194841[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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