Interactions between lipid-free apolipoprotein-AI and a lipopeptide incorporating the RGDS cell adhesion motif.

V Castelletto,I W Hamley,J Ruokolainen,M Reza

doi:10.1039/c4nr05072j

V Castelletto, I W Hamley + Show 2 more

Open Access

https://doi.org/10.1039/c4nr05072j

Copy DOI

Journal: Nanoscale	Publication Date: Jan 1, 2015
Citations: 2	License type: cc-by

Affiliation: University of Reading, Aalto University

Abstract

The interaction of a designed bioactive lipopeptide C16-GGGRGDS, comprising a hexadecyl lipid chain attached to a functional heptapeptide, with the lipid-free apoliprotein, Apo-AI, is examined. This apolipoprotein is a major component of high density lipoprotein and it is involved in lipid metabolism and may serve as a biomarker for cardiovascular disease and Alzheimers' disease. We find via isothermal titration calorimetry that binding between the lipopeptide and Apo-AI occurs up to a saturation condition, just above equimolar for a 10.7 μM concentration of Apo-AI. A similar value is obtained from circular dichroism spectroscopy, which probes the reduction in α-helical secondary structure of Apo-AI upon addition of C16-GGGRGDS. Electron microscopy images show a persistence of fibrillar structures due to self-assembly of C16-GGGRGDS in mixtures with Apo-AI above the saturation binding condition. A small fraction of spheroidal or possibly "nanodisc" structures was observed. Small-angle X-ray scattering (SAXS) data for Apo-AI can be fitted using a published crystal structure of the Apo-AI dimer. The SAXS data for the lipopeptide/Apo-AI mixtures above the saturation binding conditions can be fitted to the contribution from fibrillar structures coexisting with flat discs corresponding to Apo-AI/lipopeptide aggregates.

Highlights

Apolipoproteins are proteins that bind lipids, and are involved in lipid transport in vivo
A similar value is obtained from circular dichroism spectroscopy, which probes the reduction in α-helical secondary structure of Apolipoprotein A-I (Apo-AI) upon addition of C16-GGGRGDS
The relatively low Apo-AI concentration selected for Isothermal titration calorimetry (ITC) reduces the total number of binding sites to ensure saturation of C16GGGRGDS binding to Apo-AI is reached

Summary

Introduction

Apolipoproteins are proteins that bind lipids, and are involved in lipid transport in vivo. There are six classes of apolipoprotein with different structures and biological activities. The apoliprotein A family is a major component of high density lipoprotein (HDL). HDL removes fat and cholesterol from cells and there is significant research interest in the interaction of Apo-A apolipoproteins with lipids due to biomedical relevance, in particular to cardiovascular disease. Among this class, Apo-AI is the major component of HDL, comprising 70% of total protein.[1] Polymorphism in the gene associated with Apo-AI has been associated with early onset Alzheimer’s disease.[2]

Objectives

Methods

Results

Conclusion