ИСТИНА

Conformational changes of blood plasma proteins seem to cause a failure of its functional properties and to lead to different social important diseases. Among all plasma proteins human serum albumin (HSA) is the most studied one as it is the main transport protein and can bind a wide variety of ligands especially fatty acids. Conformational changes of albumin can be revealed in structural changes in the vicinity of binding sites, that allows one to use binding parameters as an indicator of conformational changes of protein macromolecule (e.g. metal binding assay as a tool to diognose ishemic disease [1]). To acheive better results the chosen ligand should have several specific binding sites that are located uniformly in protein structure. In the case of albumin fatty acids (FAs) can suit to this requirements as there are from 6 to 9 binding sites (depended on the type of FA) in albumin structure[2]. It should be noted that binding parameters of paramagnetic labeled FAs in human blood plasma are used to indicate pathology [3]. This method is based on the fact that paramagnetic labeled FAs binds excusevely to HSA and other types of proteins (e.g. the second abandoned protein – immunoglobulin gamma (IgG)) don't interact with it. Another ligand that induce a wide range of conformational changes in HSA and can simulate binding of FAs to HSA as well as protein denaturation is surfactant sodium dodecyl sulfate (SDS)[4]. Alterations in parameters of SDS-HSA binding was chosen here to indicate HSA conformation in blood plasma. In this paper SDS binding properties in blood plasma samples as well as in model solutions (HSA aqueous solution, IgG aqueous solution, mixed HSA and IgG aqueous solution so-called artificial plasma) were determined by means of tyrosine (Tyr) fluorescence contribution to the whole intrinsic fluorescence of investigated samples. In contrast to tryptophan (Trp) Tyr is distributed more uniform in HSA structure that allows one to detect its conformational changes far from the only one Trp residue [5]. In this article [5] we showed that Tyr fluorescence is able to detect SDS binding to the specific FA sites whereas Tpr one is independent on corresponding range of SDS concentrations. Here we compared Tyr fluorescence of blood samples as a function of SDS concentration with that of aqueous solution of the main plasma proteins (HSA and IgG) as well as that of artificial plasma/ Based on the obtained results we can conclude that at low SDS concentration (less than critical micelle concentration) changes in Tyr fluorescence can be fully explain by binding SDS to the specific bing sites of HSA while IgG seems not to contribute to plasma fluorescence response. This fact allows one to use the dependence of Tyr fluorescence on SDS concentration as a tool for pathology diognostics. [1] G. Fanali, A. di Masi, V. Trezza, M. Marino, M. Fasano, and P. Ascenzi, Human serum albumin: from bench to bedside, Molecular aspects of medicine, 33(3), 209-290 (2012). [2] A. A.Bhattacharya, T. Grüne, and S. Curry, Crystallographic analysis reveals common modes of binding of medium and long-chain fatty acids to human serum albumin. Journal of molecular biology, 303(5), 721-732, (2000). [3] V. Muravsky, T. Gurachevskaya, S. Berezenko, K. Schnurr, and A. Gurachevsky, Fatty acid binding sites of human and bovine albumins: Differences observed by spin probe ESR. Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy, 74(1), 42–47, (2009). [4] E. L. Gelamo, C. H. T. P. Silva, H. Imasato, and M. Tabak, Interaction of bovine (BSA) and human (HSA) serum albumins with ionic surfactants: spectroscopy and modelling. Biochimica et Biophysica Acta (BBA)-Protein Structure and Molecular Enzymology, 1594(1), 84- 99 (2002). [5] N.G. Zhdanova, E.A. Shirshin, E.G. Maksimov, I.M. Panchishin, A.M. Saletsky, and V.V. Fadeev, Tyrosine fluorescence probing of the surfactant-induced conformational changes of albumin. Photochemical & Photobiological Sciences, 14(5), 897-908, (2015).