title: Multidomain structure and cellulosomal localization of the Clostridium thermocellum cellobiohydrolase CbhA.
abstract: The nucleotide sequence of the Clostridium thermocellum F7 cbhA gene, coding for the cellobiohydrolase CbhA, has been determined. An open reading frame encoding a protein of 1,230 amino acids was identified. Removal of a putative signal peptide yields a mature protein of 1,203 amino acids with a molecular weight of 135,139. Sequence analysis of CbhA reveals a multidomain structure of unusual complexity consisting of an N-terminal cellulose binding domain (CBD) homologous to CBD family IV, an immunoglobulin-like beta-barrel domain, a catalytic domain homologous to cellulase family E1, a duplicated domain similar to fibronectin type III (Fn3) modules, a CBD homologous to family III, a highly acidic linker region, and a C-terminal dockerin domain. The cellulosomal localization of CbhA was confirmed by Western blot analysis employing polyclonal antibodies raised against a truncated enzymatically active version of CbhA. CbhA was identified as cellulosomal subunit S3 by partial amino acid sequence analysis. Comparison of the multidomain structures indicates striking similarities between CbhA and a group of cellulases from actinomycetes. Average linkage cluster analysis suggests a coevolution of the N-terminal CBD and the catalytic domain and its spread by horizontal gene transfer among gram-positive cellulolytic bacteria.
authors.affiliation: Institute of Molecular Genetics, Russian Academy of Science, Moscow, Russia. zverlov@biol.chemie.tu-muenchen.de
authors.forename: V V
authors.initials: VV
authors.lastname: Zverlov
authors.forename: G V
authors.initials: GV
authors.lastname: Velikodvorskaya
authors.forename: W H
authors.initials: WH
authors.lastname: Schwarz
authors.forename: K
authors.initials: K
authors.lastname: Bronnenmeier
authors.forename: J
authors.initials: J
authors.lastname: Kellermann
authors.forename: W L
authors.initials: WL
authors.lastname: Staudenbauer
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002462:Cell Membrane / Q000201:enzymology; D002480:Cellulase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D043366:Cellulose 1,4-beta-Cellobiosidase; D003013:Clostridium / Q000201:enzymology* / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid
chemical_list: D004269:DNA, Bacterial; D002480:Cellulase; D043366:Cellulose 1,4-beta-Cellobiosidase