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 A [3] or as the glycosyl hydrolases family 5 [4,E1]. The enzymes which are currently known to belong to this family are listed below.

• Endoglucanases from various species and strains of Bacillus.
• Butyrivibrio fibrisolvens endoglucanases 1 (end1) and A (celA).
• Caldocellum saccharolyticum bifunctional endoglucanase/exoglucanase (celB). This protein consists of two domains; it is the C-terminal domain, which has endoglucanase activity, which belongs to this family.
• Clostridium acetobutylicum endoglucanase (eglA).
• Clostridium cellulolyticum endoglucanases A (celccA) and D (celccD).
• Clostridium cellulovorans endoglucanase B (engB) and D (engD).
• Clostridium thermocellum endoglucanases B (celB), C (celC), E (celE), G (celG) and H (celH).
• Erwinia chrysanthemi endoglucanase Z (celZ).
• Fibrobacter succinogenes endoglucanase 3 (cel-3).
• Pseudomonas fluorescens endoglucanase C (celC).
• Pseudomonas solanacearum endoglucanase (egl).
• Robillarda strain Y-20 endoglucanase I.
• Ruminococcus albus endoglucanases I (EG-I), A (celA), and B (celB).
• Ruminococcus flavefaciens cellodextrinase A (celA).
• Ruminococcus flavefaciens endoglucanase E (celE).
• Streptomyces lividans endoglucanase.
• Thermomonospora fusca endoglucanase E-5 (celE).
• Trichoderma reesei endoglucanase II (EGLII).
• Xanthomonas campestris endoglucanase (engxcA).

As well as:

• Baker's yeast glucan 1,3-β-glucosidase I/II (EC 3.2.1.58) (EXG1).
• Baker's yeast glucan 1,3-β-glucosidase 2 (EC 3.2.1.58) (EXG2).
• Baker's yeast sporulation-specific glucan 1,3-β-glucosidase (SPR1).
• Caldocellum saccharolyticum β-mannanase (EC 3.2.1.78) (manA).
• Yeast hypothetical protein YBR056w.
• Yeast hypothetical protein YIR007w.

One of the conserved regions in these enzymes contains a conserved glutamic acid residue which is potentially involved [5] in the catalytic mechanism. We use this region as a signature pattern.