PRIMARY SEQUENCE-ANALYSIS OF CLOSTRIDIUM-CELLULOVORANS CELLULOSE BINDING PROTEIN-A

The cbpA gene for the Clostridium cellulovorans cellulose binding protein (CbpA), which is part of the multisubunit cellulase complex, has been cloned and sequenced. When cbpA was expressed in Escherichia coli, proteins capable of binding to crystalline cellulose and of interacting with anti-CbpA were observed. The cbpA gene consists of 5544 base pairs and encodes a protein containing 1848 amino acids with a molecular mass of 189,036 Da. The open reading frame is preceded by a Gram-positive-type ribosome binding site. A signal peptide sequence of 28 amino acids is present at its N terminus. The encoded protein is highly hydrophobic with extremely high levels of threonine and valine residues. There are two types of putative cellulose binding domains of almost-equal-to 100 amino acids that are slightly hydrophilic and eight conserved, highly hydrophobic beta-sheet regions of almost-equal-to 140 amino acids. These latter hydrophobic regions may be the CbpA domains that interact with the different enzymatic subunits of the cellulase complex.