STRUCTURAL BASIS OF THE PROPERTIES OF AN INDUSTRIALLY RELEVANT THERMOPHILIC XYLANASE

A thermophilic xylanase from Bacillus strain D3 suitable for use as a bleach booster in the paper pulping industry has been identified and c haracterized, The enzyme is suited to the high temperature and alkalin e conditions needed for using xylanases in the pulp industry, The xyla nase is stable at 60 degrees C and relatively stable at high temperatu res, with a temperature optimum of 75 degrees C, The pH optimum is 6, but the enzyme is active over a broad pH range, The xylanase has been cloned and sequenced, and the crystal structure has been determined, T he structure of Bacillus D3 xylanase reveals an unusual feature of sur face aromatic residues, which form clusters or ''sticky patches'' betw een pairs of molecules, These ''sticky patches'' on the surface of the enzyme are responsible for the tendency of the protein to aggregate a t high concentrations in the absence of reagents such as ethylene glyc ol, The formation of dimers and higher order polymers via these hydrop hobic contacts may also contribute to the thermostability of this xyla nase. (C) 1997 Wiley-Liss, Inc.