The microbial degradation of cellulose and xylans requires several types of enzymes such as endoglucanases (EC 3.2.1.4), cellobiohydrolases (EC 3.2.1.91) (exoglucanases), or xylanases (EC 3.2.1.8) [1,2]. Fungi and bacteria produces a spectrum of cellulolytic enzymes (cellulases) and xylanases which, on the basis of sequence similarities, can be classified into families. One of these families is known as the cellulase family D [3] or as the glycosyl hydrolases family 8 [4,E1]. The enzymes which are currently known to belong to this family are listed below.

• Acetobacter xylinum endonuclease cmcAX.
• Bacillus strain KSM-330 acidic endonuclease K (Endo-K).
• Cellulomonas josui endoglucanase 2 (celB).
• Cellulomonas uda endoglucanase.
• Clostridium cellulolyticum endoglucanases C (celcCC).
• Clostridium thermocellum endoglucanases A (celA).
• Erwinia chrysanthemi minor endoglucanase y (celY).
• Bacillus circulans β-glucanase (EC 3.2.1.73).
• Escherichia coli hypothetical protein yhjM.

The most conserved region in these enzymes is a stretch of about 20 residues that contains two conserved aspartate. The first asparatate is thought [5] to act as the nucleophile in the catalytic mechanism. We have used this region as a signature pattern.