Evolutionary and structural constraints influencing apolipoprotein A-I amyloid behavior.

Romina A Gisonno,Nahuel A Ramella,M Alejandra Tricerri,Exequiel E Barrera,Tomas Masson,Víctor Romanowski

doi:10.1002/prot.26217

Abstract

Apolipoprotein A-I (apoA-I) has a key function in the reverse cholesterol transport. However, aggregation of apoA-I single point mutants can lead to hereditary amyloid pathology. Although several studies have tackled the biophysical and structural consequences introduced by these mutations, there is little information addressing the relationship between the evolutionary and structural features that contribute to the amyloid behavior of apoA-I. We combined evolutionary studies, in silico mutagenesis and molecular dynamics (MD) simulations to provide a comprehensive analysis of the conservation and pathogenic role of the aggregation-prone regions (APRs) present in apoA-I. Sequence analysis demonstrated that among the four amyloidogenic regions described for human apoA-I, only two (APR1 and APR4) are evolutionary conserved across different species of Sarcopterygii. Moreover, stability analysis carried out with the FoldX engine showed that APR1 contributes to the marginal stability of apoA-I. Structural properties of full-length apoA-I models suggest that aggregation is avoided by placing APRs into highly packed and rigid portions of its native fold. Compared to silent variants extracted from the gnomAD database, the thermodynamic and pathogenic impact of amyloid mutations showed evidence of a higher destabilizing effect. MD simulations of the amyloid variant G26R evidenced the partial unfolding of the alpha-helix bundle with the concomitant exposure of APR1 to the solvent, suggesting an insight into the early steps involved in its aggregation. Our findings highlight APR1 as a relevant component for apoA-I structural integrity and emphasize a destabilizing effect of amyloid variants that leads to the exposure of this region.

Highlights

Apolipoprotein A-I is the most abundant protein component of high-density lipoproteins (HDL) and is responsible for the reverse cholesterol transport from extracellular tissues back to the liver [1, 2], which has been associated with a protective function against cardiac disease and atherosclerosis [3, 4]
Prolines have been extensively characterized as a fundamental component for Apolipoprotein A-I (apoA-I) flexibility and stability, as their positioning at the beginning of the 22-mers induces a relative break of one helical segment respect to the other, allowing the protein rearrangement required for lipid removal and dynamic interactions with membranes and proteins interactors [26]
Given that fast evolving regions of proteins have been associated with greater flexibility [34, 35], the higher evolutionary rate observed for the C-terminal region could be linked with the maintenance of the flexibility required for its lipid-binding properties

Summary

Introduction

Apolipoprotein A-I (apoA-I) is the most abundant protein component of high-density lipoproteins (HDL) and is responsible for the reverse cholesterol transport from extracellular tissues back to the liver [1, 2], which has been associated with a protective function against cardiac disease and atherosclerosis [3, 4]. The scaffolding functions of apoA-I in the HDL particle and its multiple protein-protein interactions, mainly with the lecithin:cholesterol acyltransferase and the ATP-binding cassette A1 transporter [5, 6], forces it to maintain a dynamic and flexible conformation [7] In contrast to these physiological functions, several point mutations affecting apoA-I have been associated with hereditary amyloid pathology [8]. Our results suggest that APR1 is a structural component that contributes to the stability of apoA-I helix bundle and emphasizes the destabilizing effect of amyloid variants, which is linked to subsequent APRs exposure in the case of G26R variant This information is relevant to understand how a marginally stable, but metabolically active protein manages to initiate the formation of an amyloid structure and develop a severe pathology

Objectives

Methods

Results

Conclusion