Influence of C-terminal truncation of murine Serum amyloid A on fibril structure

Matthies Rennegarbe,Romy Sawilla,Inga Lenter,Christian Haupt,Angelika Schierhorn

doi:10.1038/s41598-017-06419-1

Abstract

Amyloid A (AA) amyloidosis is a systemic protein misfolding disease affecting humans and other vertebrates. While the protein precursor in humans and mice is the acute-phase reactant serum amyloid A (SAA) 1.1, the deposited fibrils consist mainly of C-terminally truncated SAA fragments, termed AA proteins. For yet unknown reasons, phenotypic variations in the AA amyloid distribution pattern are clearly associated with specific AA proteins. Here we describe a bacterial expression system and chromatographic strategies to obtain significant amounts of C-terminally truncated fragments of murine SAA1.1 that correspond in truncation position to relevant pathological AA proteins found in humans. This enables us to investigate systematically structural features of derived fibrils. All fragments form fibrils under nearly physiological conditions that show similar morphological appearance and amyloid-like properties as evident from amyloid-specific dye binding, transmission electron microscopy and infrared spectroscopy. However, infrared spectroscopy suggests variations in the structural organization of the amyloid fibrils that might be derived from a modulating role of the C-terminus for the fibril structure. These results provide insights, which can help to get a better understanding of the molecular mechanisms underlying the different clinical phenotypes of AA amyloidosis.

Highlights

Amyloidosis is a group of diseases associated with the pathological deposition of amyloid fibrils in the body, including Alzheimer’s and prion diseases, type II diabetes or different systemic amyloidosis[1]
We have established recombinant expression systems and purification strategies for the production of significant quantities of C-terminal truncated fragments of serum amyloid A (SAA)(1–103) that correspond to naturally occurring Amyloid A (AA) proteins
We have systematically examined the structural features of fibrils derived from these AA proteins

Summary

Introduction

Amyloidosis is a group of diseases associated with the pathological deposition of amyloid fibrils in the body, including Alzheimer’s and prion diseases, type II diabetes or different systemic amyloidosis[1]. A great similarity exists between human and murine genes including sequence homology, the boundary position of exons and introns and the presence of several SAA polymorphisms[4, 5] These polymorphisms result only in small differences in amino acid sequence and have been described and summarized in detail elsewhere[1, 6]. We describe a recombinant expression system that enables us to obtain large quantities of C-terminally truncated fragments of full-length murine SAA1.1 This allows us to systematically investigate for the first time the influence of C-terminal truncation of murine serum amyloid A on the structural features of the derived fibrils to get insights into the mechanism of pathology of AA amyloidosis

Methods

Results

Conclusion