title: 2D-NMR reveals different populations of exposed lysine residues in the apoB-100 protein of electronegative and electropositive fractions of LDL particles.
abstract: Several potentially atherogenic LDL subfractions present low affinity for the LDL receptor, which result in impaired plasma clearance. Electronegative LDL [LDL(-)] is one of these minor subfractions and the molecular basis for its reduced receptor affinity is not well understood. In the present study, high-resolution 2D-NMR spectroscopy has been employed to characterize the surface-exposed lysine residues of the apolipoprotein (apo)B-100 protein in both LDL(-) and LDL(+) subfractions. LDL(+) showed two populations of lysine residues, similar to those previously described in total LDL. "Normal" Lys have a pk(a) of 10.4 whereas "active" Lys have a pk(a) of 8.8 and have been suggested to be involved in receptor binding. In contrast to LDL(+), the LDL(-) subfraction presented a third type of Lys, named as "intermediate" Lys, with a different microenvironment and higher basicity (pk(a) 10.7). These intermediate Lys cannot be reliably identified by 1D-NMR. Because the abundance of normal Lys is similar in LDL(+) and LDL(-), the intermediate Lys in the apoB-100 molecule of LDL(-) should come from a group of active Lys in LDL(+) particles that have a less basic microenvironment in the LDL(-) particle. These differences between LDL(+) and LDL(-) are indicative of a distinct conformation of apoB-100 that could be related to loss of affinity of LDL(-) for the LDL receptor.
authors.affiliation: CIC bioGUNE, Parque Tecnológico de Bizkaia, 48160 Derio, Spain.
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Blanco
authors.forename: Sandra
authors.initials: S
authors.lastname: Villegas
authors.forename: Sònia
authors.initials: S
authors.lastname: Benítez
authors.forename: Cristina
authors.initials: C
authors.lastname: Bancells
authors.forename: Tammo
authors.initials: T
authors.lastname: Diercks
authors.forename: Jordi
authors.initials: J
authors.lastname: Ordóñez-Llanos
authors.forename: José L
authors.initials: JL
authors.lastname: Sánchez-Quesada
mesh_terms: D053299:Apolipoprotein B-100 / Q000737:chemistry*; D050197:Atherosclerosis; D006801:Humans; D007553:Isotope Labeling; D008077:Lipoproteins, LDL / Q000737:chemistry*; D008239:Lysine; D019906:Nuclear Magnetic Resonance, Biomolecular
chemical_list: D053299:Apolipoprotein B-100; D008077:Lipoproteins, LDL; D008239:Lysine