Scaffoldin protein of cellulosome complex of cellulolytic Clostridium thermocellum bacterium have nine cohesins modules to mount nine cellulose degrading enzyme molecules. In contrast, it can express over 70 different enzymes that can degrade diverse types of cellulolytic materials into simpler soluble polysaccharides that bacteria can use. It was shown recently that to decide what enzymes to express, C. thermocellum regulates σ transcription initiation factors (used to enable specific binding of RNA polymerase to gene promoters) sensing nearby biomass composition by virtue of RsgI multi-domain trans-membrane proteins. C-terminal modules of RsgIs comprise protein modules that act as specific biosensors of specific components of biomass. Here we describe X-ray structure determination of C-terminal biomass sensor of RsgI6 of C. thermocellum in space group P21. The structure contains two molecules in asymmetric unit and was determined by molecular replacement using structure of bioinformatically detected, sequentially similar GH10 xylanase from Aspergillus nidulans. The structure represents novel fold with N-terminal and C-terminal parts of the sensor interlaced in the region of N-terminal.
