A novel family 8 psychrophilic xylanase:

fundamentals and applications

抄録

Xylanases are generally classified into glycoside hydrolase families 10 and 11 yet we have isolated eight novel cold-adapted xylanases from Antarctic and Arctic bacteria that belong to glycoside hydrolase family 8. One of these enzymes, pXyl from an Antarctic Pseudoalteromonas sp., was further studied and is found to be a very unique enzyme, displaying an (α/α)₆ barrel fold and catalysing hydrolysis with inversion of the anomeric configuration. Indeed this is the first xylanase shown to display such a structure and mechanism of action and highlights the importance of extremophilic environments as sources of novel enzymes. This enzyme is specific for xylan, is most active on long-chain xylo-oligosaccharides and in contrast to most other xylanases studied to date it is not active on aryl-β-glycosides of xylobiose or xylotriose. It displays typical characteristics for a cold-adapted enzyme: high activity at low temperatures, a reduced thermal and chemical stability and an increased flexibility as compared to a thermophilic homologous enzyme. Structural analysis indicates the basis for this adaptation as being a reduced number of salt bridges and an increased exposure of hydrophobic residues. Finally, baking trials were used to clearly demonstrate the effectiveness of all eight of the isolated xylanases as technological aids in the baking industry. Indeed, the psychrophilic characteristics (high activity at low to moderate temperatures and low stability) of this enzyme, and of psychrophilic enzymes in general, should be of much benefit in those biotechnological processes carried out at low to moderate temperatures and in particular in the food industry.