Primary Citation of Related Structures: 3WDQ, 3WDR
PubMed Abstract:
Termites and their symbiotic protists have established a prominent dual lignocellulolytic system, which can be applied to the biorefinery process. One of the major components of lignocellulose from conifers is glucomannan, which comprises a heterogeneous combination of β-1,4-linked mannose and glucose ...
Termites and their symbiotic protists have established a prominent dual lignocellulolytic system, which can be applied to the biorefinery process. One of the major components of lignocellulose from conifers is glucomannan, which comprises a heterogeneous combination of β-1,4-linked mannose and glucose. Mannanases are known to hydrolyze the internal linkage of the glucomannan backbone, but the specific mechanism by which they recognize and accommodate heteropolysaccharides is currently unclear. Here, we report biochemical and structural analyses of glycoside hydrolase family 26 mannanase C (RsMan26C) from a symbiotic protist of the termite Reticulitermes speratus. RsMan26C was characterized based on its catalytic efficiency toward glucomannan, compared with pure mannan. The crystal structure of RsMan26C complexed with gluco-manno-oligosaccharide(s) explained its specificities for glucose and mannose at subsites -5 and -2, respectively, in addition to accommodation of both glucose and mannose at subsites -3 and -4. RsMan26C has a long open cleft with a hydrophobic platform of Trp(94) at subsite -5, facilitating enzyme binding to polysaccharides. Notably, a unique oxidized Met(85) specifically interacts with the equatorial O-2 of glucose at subsite -3. Our results collectively indicate that specific recognition and accommodation of glucose at the distal negative subsites confers efficient degradation of the heteropolysaccharide by mannanase.
Related Citations:
Environmental cDNA analysis of the genes involved in lignocellulose digestion in the symbiotic protist community of Reticulitermes speratus. Todaka, N., Moriya, S., Saita, K., Hondo, T., Kiuchi, I., Takasu, H., Piero, C., Hayashizaki, Y., Kudo, T. (2007) FEMS Microbiol Ecol 59: 592
Organizational Affiliation:
Department of Biotechnology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan. Electronic address: arioka@mail.ecc.u-tokyo.ac.jp.
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