Structural studies on some dityrosine-cross-linked globular proteins: Stability is weakened, but activity is not abolished

We have carried out conformational and stability studies on three proteins that have previously been shown to undergo dityrosine (DT) cross-linking. T hey include the monomers and dimers of DT-cross-linked calmodulin and the d imers of bovine pancreatic ribonuclease A and bovine eye lens gammaB-Crysta llin. In each of these cases, we find the secondary and tertiary structure of the parent protein to be largely maintained. The DT dimer is, however, w eaker than the parent. In this sense, the properties of these DT dimers are somewhat similar to those of glutaraldehyde-cross-linked protein crystals. In contrast, the intramolecularly DT-linked monomeric protein that we stud ied (DT monomer of calmodulin) is seen to have suffered greater changes in its conformation and stability. These results gain significance in light of the growing identification of DT formation as a marker of oxidative stress , aging, and disease.