A Conserved Hydrophobic Moiety and Helix-Helix Interactions Drive the Self-Assembly of the Incretin Analog Exendin-4.

Martin Wolff,Michael Kurz,Anja Schüler,Robert Seckler,Andreas Evers,Klaus Gast,Anja Thalhammer,Stefania Pfeiffer-Marek

doi:10.3390/biom11091305

Martin Wolff, Michael Kurz + Show 6 more

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https://doi.org/10.3390/biom11091305

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Journal: Biomolecules	Publication Date: Sep 3, 2021
Citations: 1	License type: CC BY 4.0

Affiliation: University of Potsdam, Sanofi (Germany)

Abstract

Exendin-4 is a pharmaceutical peptide used in the control of insulin secretion. Structural information on exendin-4 and related peptides especially on the level of quaternary structure is scarce. We present the first published association equilibria of exendin-4 directly measured by static and dynamic light scattering. We show that exendin-4 oligomerization is pH dependent and that these oligomers are of low compactness. We relate our experimental results to a structural hypothesis to describe molecular details of exendin-4 oligomers. Discussion of the validity of this hypothesis is based on NMR, circular dichroism and fluorescence spectroscopy, and light scattering data on exendin-4 and a set of exendin-4 derived peptides. The essential forces driving oligomerization of exendin-4 are helix–helix interactions and interactions of a conserved hydrophobic moiety. Our structural hypothesis suggests that key interactions of exendin-4 monomers in the experimentally supported trimer take place between a defined helical segment and a hydrophobic triangle constituted by the Phe22 residues of the three monomeric subunits. Our data rationalize that Val19 might function as an anchor in the N-terminus of the interacting helix-region and that Trp25 is partially shielded in the oligomer by C-terminal amino acids of the same monomer. Our structural hypothesis suggests that the Trp25 residues do not interact with each other, but with C-terminal Pro residues of their own monomers.

Highlights

Insulin secretion is essentially controlled by the interaction of two incretin hormones, the glucose-dependent insulinotropic polypeptide (GIP) and the glucagon-like peptide-1 (GLP-1) with their receptors GIPR and GLP-1R, respectively
A first important matter of this work is a detailed characterization of the association state of exendin-4 under appropriate solution conditions
Our structural hypothesis (Figure 11) pictures key interactions of exendin-4 monomers in the experimentally supported trimer, which are well-rationalized by integrating our own experimental data and findings reported by Hudson et al [7]

Summary

Introduction

Insulin secretion is essentially controlled by the interaction of two incretin hormones, the glucose-dependent insulinotropic polypeptide (GIP) and the glucagon-like peptide-1(GLP-1) with their receptors GIPR and GLP-1R, respectively. The binding of all these peptides to their receptors, all members of the class B G-protein coupled receptor family, happens in a mainly α-helical conformation in a very similar manner [1]. Another commonality of these peptides is a highly conserved hydrophobic moiety FhxWL (with h denoting any hydrophobic and x denoting any amino acid, respectively) (Figure S1), which has been previously suggested to play a role in the aggregation of glucagon [2]. A major drawback hindering the pharmaceutical use of GLP-1 is its rapid degradation in vivo by the enzyme dipeptidyl-peptidase IV This has stimulated the search for peptidase

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Conclusion