Apolipoprotein A-I(R151C)Paris is defective in activation of lecithin:cholesterol acyltransferase but not in initial lipid binding, formation of reconstituted lipoproteins, or promotion of cholesterol efflux

Abstract

ApoA-I(R151)Paris is a natural apolipoprotein (apo) A-I variant that is associated with low levels of high-density lipoprotein cholesterol (HDL-cholesterol) and the partial deficiency of lecithin:cholesterol acyl-transferase (LCAT) in the plasma of heterozygous carriers. We compared the abilities of recombinant normal apoA-I and recombinant apoA-I(R151C)Paris to clear an emulsion of dimyristoylphosphatidylcholine (DMPC), to form reconstituted lipoproteins with dipalmitoylphosphatidylcholine (DPPC), to activate LCAT, and to promote efflux of biosynthetic cholesterol from porcine aortic smooth muscle cells (SMCs) or of exogenous cholesterol from lipid-loaded mouse peritoneal macrophages. Recombinant apoA-I(R151C)Paris occurred in monomeric and dimeric forms at a ratio of 60:40. Normal apoA-I and apoA-I(R151C)Paris cleared DMPC emulsions at equal rates. Both isoforms associated completely with DPPC during cholate dialysis. Normal apoA-I formed one single particle with a mean diameter of 9.3 nm, whereas apoA-I(R151)Paris gave rise to three particles with mean diameters of 9.3 nm (containing 74% of apoA-I), 10.6 nm, and 12.1 nm, respectively. Compared to normal apoA-I, apoA-I(R151C)Paris had a reduced LCAT-cofactor activity with a 60% lower Vmax/Km ratio due to a 50% higher affinity constant, Km. During incubations for 10 min and 360 min, normal apoA-I/DPPC complexes and apoA-I(R151C)Paris/DPPC complexes were equally efficient in releasing biosynthetic cholesterol from SMCs. In the lipid-free form, apoA-I(R151C)Paris induced normal hydrolysis of cholesteryl esters and normal cholesterol efflux from lipid-loaded mouse-peritoneal macrophages. In conclusion, in addition to its ability to form homo- and heterodimers, apoA-I(R151C)Paris is characterized by defective LCAT-cofactor activity but by normal lipid binding and cholesterol-efflux-promoting abilities.

High Density Lipoprotein: Assembly, Structure, Cargo, and Functions

“…The cysteine is unique to these variants as wild-type apoA-I does not contain any cysteines. However, homodimers of these variants form disulfide bonds, but this appears to have no effect on the ability to bind dimyristoylphosphatidylcholine (DMPC) or promote cholesterol efflux [41][42][43]. Although both mutations in heterozygous individuals result in decreased levels of circulating HDL, studies demonstrate the carriers are at a decreased risk of developing atherosclerosis [39,40,43].…”

Cathepsin D, a Lysosomal Protease, Regulates ABCA1-mediated Lipid Efflux

“…High density lipoprotein cholesterol (HDL-C) 3 deficiency is a major risk factor for cardiovascular diseases and has a complex metabolic and genetic etiology. Overproduction and/or impaired clearance of triglyceride-rich lipoproteins results in triglyceride enrichment of HDL and accelerated apoA-I catabolism and may account for low HDL-C in patients with other features of the metabolic syndrome.…”

Cysteine mutants of human apolipoprotein A-I: a study of secondary structural and functional properties

“…Furthermore, a clinical trial revealed that administration of recombinant A-I M /phospholipid complex (ETC-216) produced significant regression of coronary atherosclerosis (17). The abnormal coexistence of an increased risk of plasma lipoprotein spectra and a decreased risk of vascular disease was observed in another cysteine variant, apoA-I Paris , with Arg-151 substituted by cysteine (18,19). All of these data suggest that the introduction of cysteine into apoA-I endows the mutants with some particular properties, resulting in increased protection from cardiovascular risk.…”