Functional analyses of multiple lichenin-degrading enzymes from the rumen bacterium Ruminococcus albus 8

Appl Environ Microbiol. 2011 Nov;77(21):7541-50. doi: 10.1128/AEM.06088-11. Epub 2011 Sep 2.

Abstract

Ruminococcus albus 8 is a fibrolytic ruminal bacterium capable of utilization of various plant cell wall polysaccharides. A bioinformatic analysis of a partial genome sequence of R. albus revealed several putative enzymes likely to hydrolyze glucans, including lichenin, a mixed-linkage polysaccharide of glucose linked together in β-1,3 and β-1,4 glycosidic bonds. In the present study, we demonstrate the capacity of four glycoside hydrolases (GHs), derived from R. albus, to hydrolyze lichenin. Two of the genes encoded GH family 5 enzymes (Ra0453 and Ra2830), one gene encoded a GH family 16 enzyme (Ra0505), and the last gene encoded a GH family 3 enzyme (Ra1595). Each gene was expressed in Escherichia coli, and the recombinant protein was purified to near homogeneity. Upon screening on a wide range of substrates, Ra0453, Ra2830, and Ra0505 displayed different hydrolytic properties, as they released unique product profiles. The Ra1595 protein, predicted to function as a β-glucosidase, preferred cleavage of a nonreducing end glucose when linked by a β-1,3 glycosidic bond to the next glucose residue. The major product of Ra0505 hydrolysis of lichenin was predicted to be a glucotriose that was degraded only by Ra0453 to glucose and cellobiose. Most importantly, the four enzymes functioned synergistically to hydrolyze lichenin to glucose, cellobiose, and cellotriose. This lichenin-degrading enzyme mix should be of utility as an additive to feeds administered to monogastric animals, especially those high in fiber.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cloning, Molecular
  • Escherichia coli / genetics
  • Gene Expression
  • Glucans / metabolism*
  • Glycoside Hydrolases / genetics
  • Glycoside Hydrolases / isolation & purification
  • Glycoside Hydrolases / metabolism*
  • Recombinant Proteins / genetics
  • Recombinant Proteins / isolation & purification
  • Recombinant Proteins / metabolism
  • Rumen / microbiology
  • Ruminococcus / enzymology*
  • Ruminococcus / genetics
  • Ruminococcus / isolation & purification
  • Substrate Specificity

Substances

  • Glucans
  • Recombinant Proteins
  • Glycoside Hydrolases
  • lichenin