title: Association of lipids with milk α- and β-caseins.
abstract: We report the molecular interaction and the binding sites of cholesterol (CHOL), 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), dioctadecyldimethyl-ammoniumbromide (DDAB), and dioleoylphosphatidylethanolamine (DOPE) with milk α- and β-caseins in aquous solution at physiological conditions. Fourier transform infrared (FTIR), fluorescence spectroscopic methods and molecular modeling were used to determine the binding sites of lipid-protein complexes and the effect of lipid interaction on the stability and conformation of α- and β-caseins. Structural analysis showed that lipids bind casein via mainly hydrophobic contact with association constants of KCHOL-α-casein=1.0 (±0.1)×10(4) M(-1), KDOPE-α-casein=5.0 (±0.07)×10(3) M(-1), KDDAB-α-casein=2.0 (±0.06)×10(4) M(-1), KDOTAP-α-casein=1.5 (±0.6)×10(4) M(-1), KCHOL-β-casein=1.0 (±0.3)×10(4) M(-1), KDOPE-β-casein=1.5 (±0.06)×10(3) M(-1), KDDAB-β-casein=1.7 (±0.3)×10(4) M(-1) and KDOTAP-β-casein=2.1 (±0.5)×10(4) M(-1). The average number of binding sites occupied by lipid molecules on protein (n) were from 0.7 to 1.1. Docking showed different binding sites for α- and β-caseins toward lipid complexation with the free binding energies from -10 to -13 kcal/mol. Casein conformation was altered by lipid interaction with a reduction of α-helix and β-sheet and an increase of random coil and turn structure suggesting a partial protein unfolding.
  
  
  BACKGROUND
  Cascasein; CHOLcholesterol; DOTAP1,2-dioleoyl-3-trimethylammonium-propane; DDABdioctadecyldimethylammonium bromide; DOPEdioleoylphosphatidylethanolamine; FTIRFourier transform infrared spectroscopy; CDcircular dichroism.
authors.affiliation: Département de Chimie-Biologie, Université du Québec à Trois-Rivières, C.P. 500, Trois-Rivières, QC, Canada G9A 5H7.
authors.forename: P
authors.initials: P
authors.lastname: Bourassa
authors.affiliation: Département de Chimie-Biologie, Université du Québec à Trois-Rivières, C.P. 500, Trois-Rivières, QC, Canada G9A 5H7.
authors.forename: L
authors.initials: L
authors.lastname: Bekale
authors.affiliation: Département de Chimie-Biologie, Université du Québec à Trois-Rivières, C.P. 500, Trois-Rivières, QC, Canada G9A 5H7. Electronic address: tajmirri@uqtr.ca.
authors.forename: H A
authors.initials: HA
authors.lastname: Tajmir-Riahi
mesh_terms: D000818:Animals; D002364:Caseins / Q000737:chemistry* / Q000378:metabolism; D008055:Lipids / Q000737:chemistry*; D008892:Milk; D008958:Models, Molecular; D015394:Molecular Structure; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D002364:Caseins; D008055:Lipids
keywords: CD; Casein; FTIR; Lipid; Modeling; Secondary structure