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.
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