Although weak endoglucanase activity has been demonstrated in several members of this family [1-3], they lack the clustered conserved catalytic acidic amino acids present in most glycoside hydrolases. Many members of this family lack measurable cellulase activity on their own, but enhance the activity of other cellulolytic enzymes. They are therefore unlikely to be true glycoside hydrolases [4]. The substrate-binding surface of this family is a flat Ig-like fold [5]. This family of enzymes were originally classified as glycoside hydrolases (GH61) and they have been reclassified as the Auxiliary Activity Family 9 (AA9) of CAZy.

1: Development and application of a suite of polysaccharide-degrading enzymes for analyzing plant cell walls. Bauer S, Vasu P, Persson S, Mort AJ, Somerville CR; Proc Natl Acad Sci U S A. 2006;103:11417-11422. PMID:16844780

2: Homologous expression and characterization of Cel61A (EG IV) of Trichoderma reesei. Karlsson J, Saloheimo M, Siika-Aho M, Tenkanen M, Penttila M, Tjerneld F; Eur J Biochem. 2001;268:6498-6507. PMID:11737205

3: Molecular cloning and characterization of a putative cDNA encoding endoglucanase IV from Trichoderma viride and its expression in Bombyx mori. Li XH, Zhang P, Liang S, Zhou F, Wang MX, Bhaskar R, Malik FA, Niu YS, Miao YG; Appl Biochem Biotechnol. 2012;166:309-320. PMID:22057939

4: Stimulation of lignocellulosic biomass hydrolysis by proteins of glycoside hydrolase family 61: structure and function of a large, enigmatic family. Harris PV, Welner D, McFarland KC, Re E, Navarro Poulsen JC, Brown K, Salbo R, Ding H, Vlasenko E, Merino S, Xu F, Cherry J, Larsen S, Lo Leggio L; Biochemistry. 2010;49:3305-3316. PMID:20230050

5: Structural and functional characterization of a conserved pair of bacterial cellulose-oxidizing lytic polysaccharide monooxygenases. Forsberg Z, Mackenzie AK, Sorlie M, Rohr AK, Helland R, Arvai AS, Vaaje-Kolstad G, Eijsink VG; Proc Natl Acad Sci U S A. 2014;111:8446-8451. PMID:24912171