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 (FAs). There are from 6 to 9 binding sites (depended on the type of FA) in albumin structure[2]. Binding parameters of paramagnetic labeled FAs in human blood plasma are commonly used to reveal pathology [3]. This method is based on the fact that in human plasma paramagnetic labeled FAs binds exclusively to HSA and other types of proteins (e.g. the second abundant protein – immunoglobulin gamma (IgG)) don't interact with it. Thus paramagnetic response of FAs allows one to determine its binding parameters that appear to be an indicator of HSA conformational changes associated with pathology. In the present study a surfactant sodium dodecyl sulfate (SDS) was used to simulate FAs binding to HSA as it was shown in [4] by means of molecular docking. Here 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 Trp residue in II domain of HSA [5]. We also 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 binding 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 diagnostics. The reported study was supported by Russian Scientific Foundation (grant № 14-15-00602). [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).