Spectroscopic studies on the structural organization of the lectin discoidin I: homologies with fibronectin

The structure of the lectin discoidin I has been studied by circular dichroism and fluorescence spectroscopy. A positive ellipticity band at 224 nm is detected in the CD spectrum of discoidin I. The fluorescence spectra show a defined shoulder at 325 nm that through acrylamide quenching has been associated with a displaced tryptophan residue partly buried in the discoidin I molecule. This tryptophan could also be responsible for the 224 nm positive band of the CD spectrum. These spectroscopic characteristics of discoidin I indicate the existence of structural homologies with fibronectin, where the optical activity of aromatic chromophores has been associated with the positive ellipticity band at 227 nm. The CD adjust parameters and theoretical secondary structure predictions show that discoidin I is a molecule with a low content of alpha-helix and beta-strand and high content of beta-turn structures, similar to other lectins.