Fibrils of type I collagen in the skin are exposed to ultraviolet (UV) light and there have been claims that collagen photo-degradation leads to wrinkles and may contribute to skin cancers. To understand the effects of UV radiation on collagen, type I collagen solutions were exposed to the UV-C wavelength of 254 nm for defined lengths of time at 4°C. Circular dichroism (CD) experiments show that irradiation of collagen leads to high loss of triple helical content with a new lower thermal stability peak and SDS-gel electrophoresis indicates breakdown of collagen chains. To better define the effects of UV radiation on the collagen triple-helix, the studies were extended to peptides which model the collagen sequence and conformation. CD studies showed irradiation for days led to lower magnitudes of the triple-helix maximum at 225 nm and lower thermal stabilities for two peptides containing multiple Gly-Pro-Hyp triplets. In contrast, the highest radiation exposure led to little change in the Tm values of (Gly-Pro-Pro)10 and (Ala-Hyp-Gly)10, although (Gly-Pro-Pro)10 did show a significant decrease in triple helix intensity. Mass spectroscopy indicated preferential cleavage sites within the peptides, and identification of some of the most susceptible sites of cleavage. The effect of radiation on these well defined peptides gives insight into the sequence and conformational specificity of photo-degradation of collagen.

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Previously presented models of collagen-DNA (7) and collagen-siRNA (8) complexes point to a general description of delivery systems and indicate to what specific topology that system should be equipped with to effectively deliver the gene into the living body via in vivo and in vitro injection. We focused our interest on the nature of collagen-DNA complex structure and the molecular and environmental determinants of the self-association processes of collagen with the presence of DNA. In this aspect, the self-association of collagen-DNA complex offers an opportunity to characterize a unique system, which may be related to the general mechanisms of self-association of fiber macromolecules by water bridges. For characterizing the collagen-DNA interaction, we used FTIR-ATR, NMR, and AFM experiments done on a separate collagen film, DNA film, and on the peptide-DNA aqueous solution. We demonstrate that collagen-DNA spontaneously forms self-assembling complex systems in aqueous solution. Such self-association of the complex could be induced by electrostatic interactions between neutral collagen cylinders, having strong dipole moment, and negatively charged DNA cylinders. A final complex could be formed by hydrogen bonds between specified donor groups of collagen and phosphate acceptor groups of DNA. According to FTIR measurements, a collagen triple helix should not change global conformation during collagen-DNA complex formation.

The study of the influence of UV irradiation on collagen solutions has shown the destabilization of the collagen molecule by calorimetric method. It is reflected both in changes of thermodynamic parameters of transition (Tm,ΔH,Cp=f(t)) and in the appearance of a low temperature peak, that is practically irreversible against rescanning. All these indicate that the important defects in the molecule occur. The ESR measurements have shown that the above-mentioned thermal changes are connected with the occurrence of free radicals in solution under UV irradiation. They interact with proline (Pro) residues of the protein with the appearance of secondary free radicals, with following migration to glycine (Gly) residues. The emergence of the free radicals at the Pro and then at the Gly residues may cause the dramatic structural defect resulting from the UV irradiation, which significantly alters the network of hydrogen bonds in the triple helix of the collagen molecule. All this is connected with destabilization of the collagen molecule, because the defects in amino acid residues probably lead to cleavage of covalent bonds near the damaged sites maintaining the triple helical structure. The presence of ascorbic acid in collagen solution protects the collagen molecule from occurring of secondary free radicals.

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