Structural and functional analyses of the cellulase transcription regulator CeIR

CeIR is a transcriptional regulator that controls the expression of cellulases catalyzing cellulose hydrolysis. However, the structural mechanism of its regulation has remained unclear. Here, we report the first structure of CeIR. in this case with cellobiose bound. CeIR consists of a DNA-binding domain (DBD) and a regulatory domain (RD), and homodimerizes with each monomer bound to cellobiose. A hinge region (HR) in CeIR connects the DBD with the RD. and Leu59 in the HR acts as a leucine lever' that transduces a transcriptional activation signal. Furthermore, an alpha 4 helix mediates the ligand-binding signal for transcriptional activation. TyrS4 and Gln301 can potentially alter the ligand specificity of CeIR. This study provides a pivotal step toward understanding transcription of the cellulases.