2D-NMR reveals different populations of exposed lysine residues in the apoB-100 protein of electronegative and electropositive fractions of LDL particles.
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.
Blanco
Francisco J
FJ
CIC bioGUNE, Parque Tecnológico de Bizkaia, 48160 Derio, Spain.
Villegas
Sandra
S
Benítez
Sònia
S
Bancells
Cristina
C
Diercks
Tammo
T
Ordóñez-Llanos
Jordi
J
Sánchez-Quesada
José L
JL
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
D053299:Apolipoprotein B-100; D008077:Lipoproteins, LDL; D008239:Lysine