Unusual sequence organization in CenB, an inverting endoglucanase from Cellulomonas fimi.
The nucleotide sequence of the cenB gene was determined and used to deduce the amino acid sequence of endoglucanase B (CenB) of Cellulomonas fimi. CenB comprises 1,012 amino acids and has a molecular weight of 105,905. The polypeptide is divided by so-called linker sequences rich in proline and hydroxyamino acids into five domains: a catalytic domain of 607 amino acids at the N terminus, followed by three repeats of 98 amino acids each which are greater than 60% identical, and a C-terminal domain of 101 amino acids which is 50% identical to the cellulose-binding domains of C. fimi cellulases Cex and CenA. A deletion mutant of the cenB gene encodes a polypeptide lacking the C-terminal 333 amino acids of CenB. The truncated polypeptide is catalytically active and, like intact CenB, binds to cellulose, suggesting that CenB has a second cellulose-binding site. The sequence of amino acids 1 to 461 of CenB is 35% identical, with a further 15% similarity, to that of a cellulase from avocado, which places CenB in cellulase family E. CenB releases mostly cellobiose and cellotetraose from cellohexaose. Like CenA, CenB hydrolyzes the beta-1,4-glucosidic bond with inversion of the anomeric configuration. The pH optimum for CenB is 8.5, and that for CenA is 7.5.
Meinke
A
A
Department of Microbiology, University of British Columbia, Vancouver, Canada.
Braun
C
C
Gilkes
N R
NR
Kilburn
D G
DG
Miller
R C
RC
Warren
R A
RA
D000595:Amino Acid Sequence; D001483:Base Sequence; D002480:Cellulase / Q000235:genetics* / Q000378:metabolism; D002872:Chromosome Deletion; D003062:Codon / Q000235:genetics; D005798:Genes, Bacterial; D006094:Gram-Positive Bacteria / Q000201:enzymology / Q000235:genetics*; D007700:Kinetics; D008969:Molecular Sequence Data; D010944:Plants / Q000201:enzymology / Q000235:genetics; D012689:Sequence Homology, Nucleic Acid
D003062:Codon; D002480:Cellulase