|Li, Xin Liang|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 11/14/2003
Publication Date: 11/14/2003
Citation: Li, X., Ximenes, E.A., Chen, H., Cotta, M.A., Ljungdahl, L.G. 2003. Cloning and sequencing of two highly homologous cellulase genes, celh and celi from the anaerobic fungus orpinomyces strain pc-2 [abstract]. MIE Bioforum. p. 120. Interpretive Summary:
Technical Abstract: Anaerobic rumen fungi produce high levels of cellulases and hemicellulases. The enzymes hydrolyze lignocellulosic polysaccharides using cellulosomal and free-enzyme strategies. As many as 10 cellulase genes, including two new reported here from the polycentric anaerobic fungus Orpinomyces sp. strain PC-2, have been cloned and sequenced. The catalytic domains of these cellulases belong to glycoside hydrolase families 5 and 6. The two new cDNAs celH and celI, coding for cellulases CelH and CelI, have recently been isolated using fungal dockerin specific PCR amplification products as hybridization probes. CelH and CelI having 491 and 464 amino acid residues, respectively, share 91% identity on amino acid sequence level. The two mature enzymes have the same modular structure consisting of an amino terminal fungal dockerin, a linker, and a carboxy terminal family 6 catalytic domain (CD). The CDs of CelA, CelC, CelD, and CelF from the fungus also belonging to family 6 have over 55% identities between each other. In contrast, the CDs of CelH and CelI have only 34-40% amino acid identities with those of CelA, CelC, CelD, or CelF. These data reveal that multiple homologous cellulase genes are present in the genome of Orpinomyces and that the family 6 glycoside hydrolases of the fungus should be placed in 2 sub-families. This view is supported by the fact that neither celH nor celI could be expressed as active cellulase in Escherichia coli while the gene products of the other cellulases of the same family are fully functional.