Cellulose is the most abundant carbohydrate on earth and hydrolyzed by cellulases in nature. During catalysis, cellulase transfers protons to and from the oxygen atoms of the glycosidic bond and a water molecule. Since cellulose is an insoluble polymer, some kinds of cellulases, with high activity toward crystalline cellulose, move on the crystal surface with continuous hydrolysis of the molecular chain. In addition, binding and dissociation on/from the crystal surface are also important elementary steps of the reaction cycle. Recently, these interesting features of cellulases can be directly analyzed, due to the development of visualization techniques. In this chapter, we introduce (1) visualization of the protonation state of the catalytic residue by neutron crystallography, (2) visualization of processive movement on the crystal surface by high-speed atomic force microscopy , and (3) visualization of binding and dissociation events by single-molecule fluorescence microscopy.
Keywords: Cellulase; Molecular motor; Neutron crystallography; Processivity; Proton pathway; Single-molecule analysis; cellulose.