mediaposted on 17.12.2020, 00:57 by Akihiko Nakamura, Kei-ichi Okazaki, Tadaomi Furuta, Minoru Sakurai, Jun Ando, Ryota Iino
The moving mechanism of the chitinase A from a bacteria Serratia marcescens (SmChiA) is explained with illustrations and structure models. SmChiA catches the chitin molecular chain to the product binding site and stabilizes the decrystallized state of the chain. Because the chitin chain stack on the crystal surface, SmChiA moves forward and makes Michaelis complex. If hydrolysis of glycoside bond is not occurred, the chain detaches from the product site and rebinds on the crystal surface. During these states, SmChiA molecule steps forward and backward by the Brownian-motion. When the chain is hydrolyzed, the N,N'-diacetyl chitobiose is diffuse to the solvent, and the chain is shorten as 1 nm. Then, the SmChiA cannot step backward anymore. This is the 'Burnt-bride' mechanism, which makes the directionality to the movement of SmChiA. The binding state after product release is in equilibrium with the 1-nm forward stepped state. Therefore, SmChiA step forward by the Brownian-motion and make Michaelis complex again.
This moving model was constructed from the experimental results of high-speed and high-precision single molecule observation of SmChiA labeled with a gold nano particle. Please check the source article about the experimental details.