Structural and Functional Analysis of the ApolipoproteinA-I A164S Variant.

Jonathan Dalla-Riva,Jitka Petrlova,Jens O Lagerstedt

doi:10.1371/journal.pone.0143915

Abstract

Apolipoprotein A-I (apoA-I) is the main protein involved in the formation of high-density lipoprotein (HDL), it is the principal mediator of the reverse cholesterol transfer (RCT) pathway and provides cardio-protection. In addition to functional wild-type apoA-I, several variants have been shown to associate with hereditary amyloidosis. In this study we have performed biophysical and biochemical analyses of the structure and functional properties of the A164S variant of apoA-I (1:500 in the Danish general population), which is the first known mutation of apoA-I that leads to an increased risk of ischaemic heart disease (IHD), myocardial infarction and mortality without associated low HDL cholesterol levels. Despite the fact that epidemiologically IHD is associated with low plasma levels of HDL, the A164S mutation is linked to normal plasma levels of lipids, HDL and apoA-I, suggesting impaired functionality of this variant. Using biophysical techniques (e.g., circular dichroism spectroscopy and electron microscopy) to determine secondary structure, stability and pro-amyloidogenic property of the lipid free A164S apoA-I variant, our observations suggest similarity in structural properties between apoA-I WT and apoA-I A164S. However, the A164S apoA-I variant exhibits lower binding affinity to lipids but forms similar sized HDL particles to those produced by WT.

Highlights

Apolipoprotein A-I is the main protein involved in the formation of high-density lipoprotein (HDL), which is the principal mediator of the reverse cholesterol transfer (RCT) pathway and provides cardio-protection [1]
No difference was observed in amyloidophilic Thioflavin T (ThT) affinity between A164S and WT Apolipoprotein A-I (apoA-I) (Fig 1) indicating negligible transition to beta-sheet structure in the A164S variant during the extended 28 days of incubation
We have previously reported high alpha-helical and low beta-sheet content of fibrillar L178H variant which was here employed as a negative control [10] and the G26R variant with strong affinity to ThT dye was employed as a positive control (p0.05 vs. apoA-I WT after 16, 20 and 28 days of incubation; Fig 1A) [15]

Summary

Introduction

Apolipoprotein A-I (apoA-I) is the main protein involved in the formation of high-density lipoprotein (HDL), which is the principal mediator of the reverse cholesterol transfer (RCT) pathway and provides cardio-protection [1]. RCT involves the membrane proteins ATP-binding cassette A1 (ABC-A1), ATP-binding cassette G1 (ABC-G1), and scavenger receptor BI (SR-BI) that participate in cholesterol transport [2, 3]. Of RCT, HDL mediates anti-inflammatory and anti-oxidant processes [5, 6]. Numerous naturally occurring apoA-I mutants have been identified [7, 8], with the most common functional outcome being impaired interaction with LCAT or an increased propensity to form amyloids [7]. Haase et al have recently described the previously unknown A164S

Methods

Results

Conclusion