Photooxidation of tryptophan and tyrosine residues in human serum albumin sensitized by pterin: a model for globular protein photodamage in skin

REID, LARA O.; ROMAN, ERNESTO A.; THOMAS, ANDRÉS H.; DANTOLA, MARIA LAURA

BIOCHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2016 vol. 55 p. 4777 - 4786

0006-2960

Human serum albumin (HSA) is the most abundant protein in the circulatory system. The identification of oxidized albumin was reported in the skin of patients suffering from vitiligo, a depigmentation disorder where the protection against UV radiation fails due to the lack of melanin. Oxidized pterins, efficient photosensitizers under UV-A irradiation, accumulate in the skin affected by vitiligo. In this work we have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins, to induce structural and chemical changes of HSA under UV-A irradiation. Our results showed that Ptr is able to photoinduce oxidation of the protein in at least two amino acid residues: tryptophan (Trp) and tyrosine (Tyr). HSA undergoes oligomerization yielding protein structures, whose molecular weight increases with irradiation time. The protein cross-linking, due to the formation of dimers of Tyr, does not significantly affect the secondary and tertiary structures of HSA. Trp is consumed in the photosensitized process and N-formylkynurenine was identified as one of its oxidation products. The photosensitization of HSA takes place via a purely dynamic process, which involves the triplet excited state of Ptr. The results presented in this work suggest that protein photodamage mediated by endogenous photosensitizers can significantly contribute to the harmful effects of UV-A radiation on the human skin.