Structural Analysis of Human Serum Albumin Complexes with Cationic Lipids

Abstract

Human serum albumin (HSA) is a major transporter for delivering several endogenous compounds including fatty acids in vivo. Even though HSA is the primary target of fatty acid binding, the effects of cationic lipid on protein stability and conformation have not been investigated. The aim of this study was to examine the interaction of human serum albumin (HSA) with helper lipids--cholesterol (Chol) and dioleoylphosphatidylethanolamine (DOPE)--and with cationic lipids--dioctadecyldimethylammonium bromide (DDAB) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), at physiological conditions, using constant protein concentration and various lipid contents. Fourier transform infrared (FTIR), circular dichroism (CD), and fluorescence spectroscopic methods were used to analyze the lipid binding mode, the binding constant, and the effects of lipid interaction on HSA stability and conformation. Structural analysis showed that cholesterol and DOPE (helper lipids) interact mainly with HSA polypeptide polar groups and via hydrophobic moieties. Hydrophobic interactions dominate the binding of cationic lipids to HSA. The number of bound lipids (n) calculated was 1.22 (cholesterol), 1.82 (DDAB), 1.76 (DOPE), and 1.56 (DOTAP). The overall binding constants estimated were KChol=2.3 (+/-0.50)x10(3) M(-1), KDDAB=8.9 (+/-0.95)x10(3) M(-1), KDOTAP=9.1 (+/-0.90)x10(3) M(-1), and KDOPE=4.7 (+/-0.70)x10(3) M(-1). HSA conformation was stabilized by cholesterol and DOPE with a slight increase of protein alpha-helical structures, while DOTAP and DDAB induced an important (alpha-->beta) transition, suggesting a partial protein unfolding.

In Vitro DNA-Binding, Cleavage Activity with pBR322, Molecular Docking and Antiproliferative Studies of Newly Synthesized Steroidal Imidazolidine Hybrids

“…The number of steroid imidazolidines per DNA 'n' calculated [37] for (7-9) was found to be 1.13, 1.19 and 1.07, respectively indicating that compound 8 has higher DNA binding propensity in agreement with the absorption titration experiment.…”

Folic acid complexes with human and bovine serum albumins

“…The number of folic acid bound per protein (n) is calculated from log [(F 0 À F)/F] = log K S + n log [folic acid] for the static quenching (Charbonneau, Beauregard, & Tajmir-Riahi, 2009;Froehlich, Mandeville, Jennings, Sedaghat-Herati, & Tajmir-Riahi, 2009;Hasni et al, 2011;Liang, Tajmir-Riahi, & Subirade, 2008;Mandeville & Tajmir-Riahi, 2010). The linear plot of log [(F 0 À F]/ F] as a function of log [folic acid] extracted from Fig.…”

Molecular dynamics simulation studies of betulinic acid with human serum albumin

“…2a and b). It binds various endogenous and exogenous ligands including hormones, fatty acids and foreign molecules such as drugs [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Recently our group has shown that HSA binds to BA with a binding constant of K BA = 1.685±0.01×10 6 M −1 [24].…”