Lookup NU author(s): Professor Harry Gilbert
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Cellulosomes prepared by the cellulose affinity digestion method from clostridium thermocellum culture supernatant hydrolysed carob galactomannan during incubation at 60°C and pH 6.5. A recombinant phage expressing mannanase activity was isolated from a library of C. thermocellum genomic DNA constructed in λZAPII. The cloned fragment of DNA containing a putative mannanase gene (manA) was sequenced, revealing an ORF of 1767 nt, encoding a protein (mannanase A; Man26A) of 589 aa with a molecular mass of 66816 Da. The putative catalytic domain (CD) of Man26A, identified by gene sectioning and sequence comparisons, displayed up to 32% identity with other mannanases belonging to family 26. Immediately downstream of the CD and separated from it by a short proline/threonine linker was a duplicated 24-residue dockerin motif, which is conserved in all C. thermocellum cellulosomal enzymes described thus far and mediates their attachment to the cellulosome-integrating protein (CipA). Man26A consisting of the CD alone (Man26A') was hyperexpressed in Escherichia coli BL21(DE3) and purified. The truncated enzyme hydrolysed soluble and insoluble mannan, displaying a temperature optimum of 65°C and a pH optimum of 6.5, but exhibited no activity against other plant cell wall polysaccharides. Antiserum raised against Man26A' cross-reacted with a polypeptide with a molecular mass of 70,000 Da that is part of the C. thermocellum cellulosome. A second variant of Man26A containing the N-terminal segment of 130 residues and the CD (Man26A') bound to ivory-nut mannan and weakly to soluble Carob galactomannan and insoluble cellulose. Man26A' consisting of the CD alone did not bind to these polysaccharides. These results indicate that the N-terminal 130 residues of mature Man26A may constitute a weak mannan-binding domain. Sequence comparisons revealed a lack of identity between this region of Man26A and other polysaccharide-binding domains, but significant identity with a region conserved in the three family 26 mannanases from the anaerobic fungus Piromyces equi.
Author(s): Halstead JR, Vercoe PE, Gilbert HJ, Davidson K, Hazlewood GP
Publication type: Article
Publication status: Published
Print publication date: 01/11/1999
ISSN (print): 13500872
ISSN (electronic): 1465-2080
Publisher: Society for General Microbiology
PubMed id: 10589717