Supramolecular Amyloid-like Assembly of the Polypeptide Sequence Coded by Exon 30 of Human Tropoelastin

Antonio Mario Tamburro,Antonietta Pepe,Brigida Bochicchio,Daniela Quaglino,Ivonne Pasquali Ronchetti

doi:10.1074/jbc.m411617200

Abstract

Elastin is known to self-aggregate in twisted-rope filaments. However, an ultrastructural organization different from the fibrils typical of elastin, but rather similar to those shown by amyloid networks, is shown by the polypeptide sequence encoded by exon 30 of human tropoelastin. To better understand the molecular properties of this sequence to give amyloid fibers, we used CD, NMR, and FTIR (Fourier transform infrared spectroscopy) to identify the structural characteristics of the peptide. In this study, we have demonstrated, by FTIR, that antiparallel beta-sheet conformation is predominant in the exon 30 fibers. These physical-chemical studies were combined with transmission electron microscopy and atomic force microscopy to analyze the supramolecular structure of the self-assembled aggregate. These studies show the presence of fibrils that interact side-by-side probably originating from an extensive self-interaction of elemental cross beta-structures. Similar sequences, of the general type XGGZG(X, Z = V, L, A, I), are widely found in many proteins such as collagens IV and XVII, major prion protein precursor, amyloid beta A4 precursor protein-binding family, etc., thus suggesting that this sequence could be involved in contributing to the self-assembly of amyloid fibers even in other proteins.

Highlights

Elastin is the protein responsible for the elasticity of skin, arteries, and lung whose elastic properties and resilience depend on its supramolecular organization and cross-linking into fibers and lamellae [1,2,3,4]
An ultrastructural organization different from the fibrils typical of elastin, but rather similar to those shown by amyloid networks, is shown by the polypeptide sequence encoded by exon 30 of human tropoelastin
Miao et al [8] have found that some mutated polypeptide sequences encoded by exons of human tropoelastin exhibit an ultrastructural organization different from the fibrils typical of elastin but rather similar to those found for amyloid networks, constituted by helical fibrils several microns long and about 10 nm wide [9]

Summary

Introduction

Elastin is the protein responsible for the elasticity of skin, arteries, and lung whose elastic properties and resilience depend on its supramolecular organization and cross-linking into fibers and lamellae [1,2,3,4]. Miao et al [8] have found that some mutated polypeptide sequences encoded by exons of human tropoelastin exhibit an ultrastructural organization different from the fibrils typical of elastin but rather similar to those found for amyloid networks, constituted by helical fibrils several microns long and about 10 nm wide [9]. Kozel et al [10] have demonstrated that a polypeptide consisting of the sequence coded by exon 30 of bovine tropoelastin formed amyloid-like fibrils. We found that the sequence encoded by exon 30 (EX30) of human tropoelastin is the only sequence in the molecule whose CD spectra roughly resemble a ␤-sheet conformation [19] and that the conformation of EX30 peptide is temperature- and concentration-dependent [20]

Methods

Results

Conclusion