Three-dimensional structure of a thermostable native cellobiohydrolase, CBH IB, and molecular characterization of thecel7gene from the filamentous fungus,Talaromyces emersonii.

The X-ray structure of native cellobiohydrolase IB (CBH IB) from the filamentous fungusTalaromyces emersonii, PDB 1Q9H, was solved to 2.4 Å by molecular replacement. 1Q9H is a glycoprotein that consists of a large, single domain with dimensions of≈ 60 Å × 40 Å × 50 Å and an overallβ-sandwich structure, the characteristic fold of Family 7 glycosyl hydrolases (GH7). It is the first structure of a native glycoprotein and cellulase from this thermophilic eukaryote. The long cellulose-binding tunnel seen in GH7 Cel7A fromTrichoderma reeseiis conserved in 1Q9H, as are the catalytic residues. As a result of deletions and other changes in loop regions, the binding and catalytic properties ofT. emersonii1Q9H are different. The gene (cel7) encoding CBH IB was isolated fromT. emersoniiand expressed heterologously with an N-terminal polyHis-tag, inEscherichia coli. The deduced amino acid sequence ofcel7is homologous to fungal cellobiohydrolases in GH7. The recombinant cellobiohydrolase was virtually inactive against methylumberiferyl-cellobioside and chloronitrophenyl-lactoside, but partial activity could be restored after refolding of the urea-denatured enzyme. Profiles ofcel7expression inT. emersonii, investigated by Northern blot analysis, revealed that expression is regulated at the transcriptional level. Putative regulatory element consensus sequences for cellulase transcription factors have been identified in the upstream region of thecel7genomic sequence. [ABSTRACT FROM AUTHOR]