The N-terminal family 22 carbohydrate-binding module of xylanase 10B of Clostridium themocellum is not a thermostabilizing domain

Xylanase Xyn10B from Clostridium thermocellum is a modular enzyme that contains two family 22 carbohydrate binding modules N- (CBM22-1) and C- (CBM22-2) terminal of the family 10 glycoside hydrolase catalytic domain (GH10). In a previous study, we showed that removal of CBM22-1 reduces the resistance to thermoinactivation of the enzyme suggesting that this module is a thermostabilizing domain. Here, we show that it is the module border on the N-terminal side of GH10 that confers resistance to thermoinactivation and to proteolysis. Therefore, CBM22-1 does not function as a thermostabilizing domain and the role for this apparently non-functional CBM remains elusive.