Dissolved organic matter in water of Daugava river

Relative quantum yieldRelative quantum yieldResonance Energy Transfer Study of Lipid Bilayer Interactions ofApolipoprotein A-I VariantsG.Gorbenko *1 , V.Trusova 1 , E.Adachi 2 , C.Mizuguchi 2 , H.Saito 21 V.N. Karazin Kharkov National University, Kharkov, Ukraine;2 Institute of Health Biosciences, The University of Tokushima, Tokushima, Japane-mail: galyagor@yahoo.comDue to its explicit distance dependence fluorescence resonance energy transfer (FRET)has long been used for obtaining structural information on a wide variety of biomolecularassemblies. In the present study this technique was employed to gain further insights intolipid interactions of apolipoprotein A-I (apoA-I) variants. ApoA-I is the main proteincomponent of high-density lipoproteins promoting cholesterol efflux from plasmamembrane and modulating phospholipid metabolism. Moreover, specific variants ofhuman apoA-I, particularly those having G26R substitution mutation, are capable offorming amyloid fibrils associated with renal or liver failure. The N-terminal fragment(amino acids 1-83) has been identified as the predominant form of apoA-I in amyloidfibril deposits. This fragment contains three tryptophan residues, Trp 8 , Trp 50 and Trp 72which have been recruited in this work as energy donors for membrane fluorescent probes4-dimethylaminochalcone (DMC) and 3-methoxybenzanthrone (MBA), located in theinterfacial bilayer region. Small unilamellar vesicles were prepared by extrusion techniquefrom egg phosphatidylcholine (PC) and its mixture with cholesterol(Chol) (30 mol%).Shown in Fig. 1 are typical FRET profiles obtained for 5 apoA-I 1-83 fragments, referredto here as apoA83 (without mutation), G26R, G26R/W8F_W50F, G26R/W8F_W72F andG26R/W50F_W72F.1.11.00.90.80.70.60.50.40.3G26R/W8F_W72F0.20 1 2 3 4 5 6Bound DMC, MG26R ApoA83G26R/W8F_W50FG26R/W50F_W72F0.40 1 2 3 4 5 6Bound DMC, MAFig. 1. FRET profiles for Trp-DMC donor-acceptor pair in PC (A) and PC/Chol (B)liposomes1.00.90.80.70.60.5G26R ApoA83G26R/W8F_W50FG26R/W50F_W72FG26R/W8F_W72FBFRET data have been quantitatively interpreted in terms of the model of energy transfer intwo-dimensional systems allowing for distance dependence of orientation factor. It wasfound that in PC membranes Trp residues adopt interfacial bilayer location, while inPC/Chol membranes they tend to reside in the aqueous phase. These findings support thehypothesis that Chol can affect the curvature of lipid-water interface in such a manner thatthermodynamically favorable location of apoA-I becomes less buried.This work was supported by the grants from European Social Fund (project number2009/0205/1DP/1.1.1.2.0/09/APIA/VIAA/152) and Fundamental Research State Fund ofUkraine (project number F.41.4/014).- 24 -