Textor LC, Colussi F, Silveira RL, Serpa V, de Mello BL, Muniz JR, Squina FM, Pereira N Jr, Skaf MS, Polikarpov I.
Aiming to contribute towards the characterization of new, biotechnologically relevant cellulolytic enzymes, we report here the first crystal structure of the catalytic core domain of Cel7A (CBHI) from the filamentous fungus Trichoderma harzianum IOC 3844. Our structural studies and molecular dynamics simulations show that the flexibility of Tyr260, in comparison to the Tyr247 from the homologous T. reesei Cel7A, is enhanced due to the short side chains of adjacent Val216 and Ala384 residues and creates an additional gap at the side face of the catalytic tunnel. T. harzianum CBHI also has a shortened loop at the entrance of the cellulose-binding tunnel, which has been described to interact with the substrate in T. reesei Cel7A. These structural features might explain why T. harzianum enzyme displays higher kcat and Km values and lower product inhibition on both glucosides and lactosides substrates as compared to T. reesei Cel7A.