ИСТИНА

Conformational changes of proteins seem to cause the failure of its functions and thus accompanied different diseases. Serum albumins are the most abundant proteins in human blood plasma and are the main carriers of different ligands (fatty acids, drugs, metabolites) [1]. The ability of binding a wide variety of ligands by albumin and as a consequence its correct activity directly depend on the protein conformation, thus the development of new indicators of albumin conformation is important for clinical application as well as for fundamental science. One of the common techniques for investigation of protein structure is fluorescence spectroscopy that is applied to intrinsic fluorophores or extrinsic labels. Among intrinsic fluorophores - tryptophan (Trp), tyrosine (Tyr) and phenylalanine – the photophysical parameters of the first one are usually used as it can be selectively excited at 295 nm [2] and its quantum yield is the highest [1]. Unfortunately there is only little amount of Trp residues in proteins, e.g. bovine serum albumin (BSA) has only two Trp residues [3] while human serum albumin (HSA) has the sole Trp [4]. In contrast to Trp Tyr residues are generally presented in HSA in a greater number and are distributed uniformly in its structure that allows one to detect its conformational changes far from the only Trp residue in II domain of HSA [5]. In the present study we investigated sensitivity of Tyr fluorescence to conformational changes of BSA and HSA. It was shown that Tyr fluorescence increases during denaturation by surfactants (cationic and anionic) and guanidine hydrochloride. In the latter case Tyr fluorescence could reveal conformational changes in domain III that don’t influence on Trp fluorescence. Also the alterations in the network of hydrogen bonds in the first hydration sphere by ethanol lead to increase Tyr fluorescence. Based on these results we conclude that Tyr fluorescence increase is usually caused by structural rearrangements in the vicinity of this kind of residues while the role of the decrease of fluorescence resonance energy transfer (FRET) to Trp is overestimated. The reported study was supported by Russian Foundation of Basic Research (grant № 16-32-00804). [1] T. Peters Jr., Serum Albumin, Adv. Protein. Chem., 1985, 37, 161-245. [2] Fasman G. D., Sober H. A. et al. Handbook of biochemistry and molecular biology. - CRC press Cleveland, 1977. - Vol. 1. [3] K.A. Majorek, P.J. Porebski, A. Dayal, M.D. Zimmerman, K. Jablonska, A.J. Stewart, M. Chruszcz, W. Minor, Structural and immunologic characterization of bovine, horse, and rabbit serum albumins, Mol. Immunol., 2012, 52 (3), 174-182. [4] S. Sugio, A. Kashima, S. Mochizuki, M. Noda, K. Kobayashi, Crystal structure of human serum albumin at 2.5 Å resolution, Protein Engineering, Design & Selection, 1999, 12 (6), 439-446. [5] N.G. Zhdanova, E.A. Shirshin, E.G. Maksimov, I.M. Panchishin, A.M. Saletsky, V.V. Fadeev, Tyrosine fluorescence probing of surfactant-induced conformational changes of albumin, Photochem. Photobiol. Sci., 2015, 14, 897-908.