Role of His-His interaction in Ser-His-Tyr sequence of chondroitinase ABC I in the enzyme activity and stability.

Despite clinical importance of chondroitinase ABC I, its application has been limited due to thermal instability as reported in the literature. There are various approaches to improve thermal stability of enzymes, among them, His-His interactions are believed generally as an effective means. In the present study and for preparing a His-His interaction, various mutations in the sequence of Ser-His-Tyr at catalytic domain of the enzyme were performed using site directed mutagenesis method. The effect of these mutations on activity, stability and structural features of cABC I was assessed. The study showed that establishment of His475-His476 pair in cABC I, did not improve thermal stability of the enzyme and inactivated it. The study also revealed the existence a hydrogen bond network in the central domain of the enzyme with a specific role for tyrosine 476. In this network, replacement of His with Ala and Try with His and Ala, deactivated and destabilized the enzyme; confirming their importance in the enzyme catalysis and stability. Also, it was found that Tyr has some important role in substrate binding, an issue which should be more investigated.