Human Islet Amyloid Polypeptide Fibril Binding to Catalase: A Transmission Electron Microscopy and Microplate Study

Nathaniel G N Milton,J Robin Harris

doi:10.1100/tsw.2010.73

Abstract

The diabetes-associated human islet amyloid polypeptide (IAPP) is a 37-amino-acid peptide that forms fibrils in vitro and in vivo. Human IAPP fibrils are toxic in a similar manner to Alzheimer's amyloid-β (Aβ) and prion protein (PrP) fibrils. Previous studies have shown that catalase binds to Aβ fibrils and appears to recognize a region containing the Gly-Ala-Ile-Ile sequence that is similar to the Gly-Ala-Ile-Leu sequence found in human IAPP residues 24-27. This study presents a transmission electron microscopy (TEM)—based analysis of fibril formation and the binding of human erythrocyte catalase to IAPP fibrils. The results show that human IAPP 1-37, 8-37, and 20-29 peptides form fibrils with diverse and polymorphic structures. All three forms of IAPP bound catalase, and complexes of IAPP 1-37 or 8-37 with catalase were identified by immunoassay. The binding of biotinylated IAPP to catalase was high affinity with a KD of 0.77nM, and could be inhibited by either human or rat IAPP 1-37 and 8-37 forms. Fibrils formed by the PrP 118-135 peptide with a Gly-Ala-Val-Val sequence also bound catalase. These results suggest that catalase recognizes a Gly-Ala-Ile-Leu—like sequence in amyloid fibril-forming peptides. For IAPP 1-37 and 8-37, the catalase binding was primarily directed towards fibrillar rather than ribbon-like structures, suggesting differences in the accessibility of the human IAPP 24-27 Gly-Ala-Ile-Leu region. This suggests that catalase may be able to discriminate between different structural forms of IAPP fibrils. The ability of catalase to bind IAPP, Aβ, and PrP fibrils demonstrates the presence of similar accessible structural motifs that may be targets for antiamyloid therapeutic development.

Highlights

The islet amyloid polypeptide (IAPP), or amylin peptide, is a hallmark of Type II diabetes mellitus (DM) pathology where it forms amyloid deposits[1,2,3]
Fibrillogenesis of IAPP can be studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM)
The sheet-like structures described are similar to those we have previously described for Aβ 17-28[11], and we have previously suggested that Aβ ribbons are aggregates of fibrils and may represent intermediates between fibril and sheet forms; similar observations may apply to IAPP fibrils, ribbons, and sheets

Summary

Introduction

The islet amyloid polypeptide (IAPP), or amylin peptide, is a hallmark of Type II diabetes mellitus (DM) pathology where it forms amyloid deposits[1,2,3]. The IAPP readily aggregates both in vitro[4,5,6] and in Milton/Harris: Human Islet Amyloid Polypeptide Fibril Binding to Catalase. TheScientificWorldJOURNAL (2010) 10, 879–893 vivo[7] to form amyloid fibrils that can be readily studied using electron microscopy[8]. Fibrillogenesis of IAPP can be studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Polymorphism of IAPP fibrils, Alzheimer’s amyloid-β (Aβ) fibrils, and the prion protein (PrP) fibrils is influenced by the environment in which the fibrillogenesis occurs[9,10,11,12,13]. The catalase 400-409 region is within the wrapping loop that may play a role in the formation of the tetramer structure[26] and should be accessible to Aβ or related peptides

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Conclusion