Abstract
To date, many GH74 family xyloglucanases have been identified and divided into three modes of activity: exo, endo-dissociative, and endo-processive. Recently, crystal structure analysis and homology modeling have determined the key structures and amino acid residues for exo and endo-processive GH74 xyloglucanase activities. For example, Geotrichum OXG-RCBH, an exo mode enzyme, has an exo-loop that blocks one side of the active site cleft and is essential for exo-mode activity. In addition, Paenibacillus XEG74, an endo-processive mode enzyme, has characteristic tryptophan residues at positive subsites of the active site cleft. These tryptophan residues are vital for endo-processive-type activity, and mutation in these tryptophan residues results in a change from endo-processive to endo-dissociative activity. In this review, we focus on the structures and modes of activity of GH74 family xyloglucanases.
