Functional and structural characterization of an α-L-arabinofuranosidase from Thermothielavioides terrestris and its exquisite domain-swapped β-propeller fold crystal packing

The fungus Thermothielavioides terrestris plays an important role in the global carbon cycle with enzymes capable of degrading polysaccharides from biomass, therefore an attractive source of proteins to be investigated and understood. From cloning to a three-dimensional structure, we foster a deeper characterization of an alpha-L-arabinofuranosidase, a glycoside hydrolase from the family 62 (TtAbf62), responsible to release arabinofuranose from non-reducing ends of polysaccharides. TtAbf62 was tested with synthetic (pNP-Araf) and polymeric substrates (arabinan and arabinoxylan), showing optimal temperature and pH (for pNP-Araf) of 30 degrees C and 4.5-5.0, respectively. Kinetic parameters revealed different specific activity for the three substrates, with a higher affinity for pNP-Araf (K-M: 4 +/- 1 mM). The hydrolyzing activity of TtAbf62 on sugarcane bagasse suggests high efficiency in the decomposition of arabinoxylan, abundant hemicellulose presented in the sugarcane cell wall. The crystal packing of TtAbf62 reveals an exquisite domain swapping, located at the supramolecular arrangement through a disulfide bond. All crystallographic behaviors go against its monomeric state in solution, indicating a crystal-induced artifact. Structural information will form the basis for further studies aiming the development of optimized enzymatic properties to be used in biotechnological applications.