Molecular Anatomy of Polysaccharide-degrading Enzymes from Extremophiles

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Many microorganisms have been discovered at unusual environments such as extreme temperature, pH and salinity. These microorganisms are called "extremophiles" that include thermophiles, psychrophiles, acidophiles, alkaliphiles and halophiles. "Extremozymes" are the enzymes produced by extremophiles and able to function under the extreme conditions. Extremozymes have tremendous potential for industrial applications as well as academic directions. Hemicellulose, originally named for the fraction extracted from plant cell walls with dilute alkali, is one of the most abundant polysaccharide in plant cell walls. Beta-1,4-Xylan is the major component of hemicelluloses ; it accounts for approximately 10 to 30% of the total dry weight of wood. Xylan is a heterogeneous polysaccharide comprising a backbone of beta-1,4- linked xylopyranose units with branches containing acetyl, L-arabino-furanosyl and glucopyranosyl residues. Xylanase (1,4-beta-D-xylan xylanohydrolase ; EC 3.2.1.8) catalyzes the hydrolysis of xylan to xylooligosaccharides and xylose. Alkaliphilic Bacillus sp. strain 41M-1 secretes a xylanase (xylanase J) that has an alkaline pH optimum. Xylanase J is a multidomain enzyme that consists of a family 11/G catalytic domain and a xylan-binding domain. Mutational analyzes revealed some amino acid residues that contribute to catalytic activity, alkaliphily and xylan-binding activity of xylanase J.