Expression, cross-linking and characterization of recombinant chitin binding resilin

Resilin is a polymeric rubber-like protein secreted by insects to specialized cuticle regions, in areas where high resilience and low stiffness are required. Resilin binds to the cuticle polysaccharide chitin via a chitin binding domain and is further polymerized through oxidation of the tyrosine residues resulting in the formation of dityrosine bridges and assembly of a high-performance protein-carbohydrate composite material. We describe for the first time a comprehensive study on the mechanical, structural and biochemical function of chitin binding recombinant Drosophila melanogaster resilin. Various resilin constructs were cloned including the full length gene enabling Ni-NTA purification, as well as heat and salt precipitation for rapid and efficient purification. The binding isotherms and constants (K_d, B_max) of resilin to chitin via its chitin binding domain were determined and displayed high affinity to chitin, implying its important role in the assembly of the resilin-chitin composite. The structural and elastic properties were investigated using Fourier Transform Infrared Spectroscopy (FTIR), Circular Dichroism (CD) and Atomic Force Microscopy (AFM) with peroxidase crosslinked solid resilin materials. Generally, little structural organization was found by these biophysical methods, suggesting structural order was not induced by the dityrosine crosslinks. Further, the elastomeric properties found from the full length protein compared favorably with the shorter resilin generated previously from exon 1. The unusual elastomeric behavior of this protein suggests possible utility in biomaterials applications.