The fibrillogenic L178H variant of apolipoprotein A-I forms helical fibrils

Jitka Petrlova,Trang Duong,Megan C Cochran,Annika Axelsson,Matthias Mörgelin,Linda M Roberts,Jens O Lagerstedt

doi:10.1194/jlr.m020883

Jitka Petrlova, Trang Duong + Show 5 more

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https://doi.org/10.1194/jlr.m020883

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Abstract

A number of amyloidogenic variants of apoA-I have been discovered but most have not been analyzed. Previously, we showed that the G26R mutation of apoA-I leads to increased β-strand structure, increased N-terminal protease susceptibility, and increased fibril formation after several days of incubation. In vivo, this and other variants mutated in the N-terminal domain (residues 26 to ∼90) lead to renal and hepatic accumulation. In contrast, several mutations identified within residues 170 to 178 lead to cardiac, laryngeal, and cutaneous protein deposition. Here, we describe the structural changes in the fibrillogenic variant L178H. Like G26R, the initial structure of the protein exhibits altered tertiary conformation relative to wild-type protein along with decreased stability and an altered lipid binding profile. However, in contrast to G26R, L178H undergoes an increase in helical structure upon incubation at 37°C with a half time (t1/2) of about 12 days. Upon prolonged incubation, the L178H mutant forms fibrils of a diameter of 10 nm that ranges in length from 30 to 120 nm. These results show that apoA-I, known for its dynamic properties, has the ability to form multiple fibrillar conformations, which may play a role in the tissue-specific deposition of the individual variants.

Highlights

A number of amyloidogenic variants of apoA-I have been discovered but most have not been analyzed
leucine to histidine mutation at residue 178 (L178H) exhibit about a 4-fold increase in binding 1-Anilinonaphthalene-8-sulfonic acid (ANS) (Fig. 1A) and a 2-fold increase for glycine to arginine mutation at residue 26 (G26R), indicating that both mutations alter apoA-I structure in a manner that increases the fraction of residues accessible to bind hydrophobic dyes
We did not detect in L178H a fragment observed in both WT and G26R that is produced by cleavage at the extreme carboxy-terminus, near residue 225

Summary

Introduction

A number of amyloidogenic variants of apoA-I have been discovered but most have not been analyzed. We showed that the G26R mutation of apoA-I leads to increased ␤-strand structure, increased N-terminal protease susceptibility, and increased fibril formation after several days of incubation. Amyloid-forming variants of apoA-I are found to accumulate in different tissues and wild-type (WT) apoA-I is present in atherosclerotic lesions as well as tissues [2,3,4] This presents a point of concern for HLDbased infusion therapies as repeated infusions could result in vascular deposition of excess A-I and thereby counter the therapeutic aim. We reported the first analysis of the structure of an amyloid apoA-I, G26R (apoA-IIOWA) [6] This variant exhibits increased ␤-strand content, N-terminal protease sensitivity, and binding to amyloid-detecting dyes as well as altered lipid-binding properties.

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