Structure of full-length bacterial chitinase containing two fibronectin type III domains revealed by small angle X-ray scattering

Chitinase A1 (ChiA1) from Bacillus circulans WL-12 consists of an N-terminal catalytic domain, two fibronectin type III domains (FnIIIDs), and a C-terminal chitin-binding domain. The full-length structure of ChiA1 was studied by small angle X-ray scattering. The obtained low-resolution structure showed that ChiA1 is an elongated molecule with a length of ∼145 Å composed of a large globular head and a rod-like tail. Combination with known high-resolution structures of individual ChiA1 domains provided a model of the domain arrangement. In this model, two FnIIIDs connect to each other in an extended rod-like shape without large bending between the FnIIIDs, and contribute largely to the length of ChiA1.