Aspergillus enzymes involved in degradation of plant cell wall polysaccharides

Abstract

Degradation of plant cell wall polysaccharides is of major importance in the food and feed, beverage, textile, and paper and pulp industries, as well as in several other industrial production processes. Enzymatic degradation of these polymers has received attention for many years and is becoming a more and more attractive alternative to chemical and mechanical processes. Over the past 15 years, much progress has been made in elucidating the structural characteristics of these polysaccharides and in characterizing the enzymes involved in their degradation and the genes of biotechnologically relevant microorganisms encoding these enzymes. The members of the fungal genus Aspergillus are commonly used for the production of polysaccharide-degrading enzymes. This genus produces a wide spectrum of cell wall-degrading enzymes, allowing not only complete degradation of the polysaccharides but also tailored modifications by using specific enzymes purified from these fungi. This review summarizes our current knowledge of the cell wall polysaccharide-degrading enzymes from aspergilli and the genes by which they are encoded.

FIG. 1

Schematic presentation of the repeating units of the two major xyloglucan structures.

FIG. 2

Schematic presentation of xylan.

FIG. 3

Schematic presentation of galactomannan.

FIG. 4

Schematic presentation of the two galactoglucomannan structures.

FIG. 5

Schematic presentation of the hairy region of pectin.

FIG. 6

Schematical presentation of ferulic acid and diferulic acid structures identified in plant cell walls.

FIG. 7

Model for the role of XlnR and CreA in the regulation of the genes encoding (hemi)cellulose-degrading enzymes by A. niger. Other regulatory factors, such as the HAP complex and PacC, are not considered in this model. UAS, Upstream Activating Sequence; URS, Upstream Repressing Sequence. (Reprinted from reference with permission of the publisher.)