Disulfide bond: a critical element in the structure and function of a collagen IV-derived antiangiogenic peptide

Antiangiogenic peptides prevent tumor growth and metastasis by inhibiting new blood vessel formation around tumors. A study demonstrated that a fragment resulting from Arresten, which contains a disulfide bond, effectively induced apoptosis and prohibited the movement and tube-like structure formation of endothelial cells and colon cancer progression in mice. The current study examined the effect of cysteine to isoleucine substitution on the function of the mutated peptide, termed LFI, in vitro and in vivo. Besides, the 2D structure and conformational changes were analyzed by Far-UV Circular Dichroism (CD) spectroscopy, molecular dynamics, and docking simulations. 60 µM of LFI reduced the migration of HUVECs by 23% and induced 32% apoptosis. The peptide up-regulated p53 and CASP9 gene expressions in HUVECs without affecting the CASP8 and BCL2 expressions. Also, LFI reduced colon carcinoma growth in mice by 15.5%. CD analysis revealed that the peptide contained 61% random coil and 39% β-turn. The first and the last LFI´s residues fluctuated more, and the average Root Mean Square Fluctuation (RMSF) for all residues was 0.36 Å. The higher Radius of Gyration (Rg) value for the peptide demonstrates a less compact conformation. This study found that eliminating disulfide bonds reduced the antimigration, antitumor, and somewhat pro-apoptotic activities of the peptide. These probably occurred through the reduction of regular secondary structures and packed conformations and the elevation of structural flexibility compared with the native peptide. This study highlights the impact of disulfide bonds in the structure-function relationship of peptide fragments, which may contribute to designing new peptide drugs.