Comparison of Primary, Secondary and Tertiary Structures of Xylanase of Bacillus pumilus and Cellulase of Aspergillus acleatus

Cellulose and xylan are two main components of plant cell mass and are polysaccharides polymerized mainly by β-l,4-glycosylic linkage. The major difference between the two is that the sugar unit of cellulose is glucose while that of xylan is xylose. The chemical difference of these two sugar moieties is that one of the hydrogen atom of xylose at carbon 5 is replaced by a hydroxymethyl group in glucose. From the similarity of chemical structure of xylan and cellulose, it is interesting to compare the enzymes acting on these two polysaccharides. We have cloned and sequenced the genes coding xylanase of Bacillus pumilus IPO and cellulase of Aspergillus acleatus and have succeeded in solving the tertiary structure of these enzymes by X-ray crystallographic analysis. In this paper, I will discuss the homology of the tertiary structures though no significant homology in the amino acid sequence is observed.