Drug-induced activation of integrin alpha IIb beta 3 leads to minor localized structural changes

TL;DR

This study investigates how drug-induced activation of integrin alphaIIb beta3 causes minimal structural changes, using biophysical and computational methods to understand conformational dynamics in a membrane environment.

Contribution

It provides new insights into integrin activation mechanisms and introduces a novel experimental approach for studying membrane proteins in relevant conditions.

Findings

Mn2+ induces active integrin conformation without major secondary structure changes.

Clinically relevant drugs activate integrin with minimal secondary structural alterations.

Minor local structural changes are observed via molecular dynamics simulations.

Abstract

Integrins are transmembrane proteins involved in hemostasis, wound healing, immunity and cancer. In response to intracellular signals and ligand binding, integrins adopt different conformations: the bent (resting) form; the intermediate extended form; and the ligand-occupied active form. An integrin undergoing such conformational dynamics is the heterodimeric platelet receptor alphaIIbbeta3. Although the dramatic rearrangement of the overall structure of alphaIIbbeta3 during the activation process is potentially related to changes in the protein secondary structure, this has not been investigated so far in a membrane environment. Here we examine the Mn2+- and drug-induced activation of alphaIIbbeta3 and the impact on the structure of this protein reconstituted into liposomes. By quartz crystal microbalance with dissipation monitoring and activation assays we show that Mn2+ induces binding of the conformation-specific antibody PAC-1, which only recognizes the extended, active integrin. Circular dichroism spectroscopy reveals, however, that Mn2+-treatment does not induce major secondary structural changes of alphaIIbbeta3. Similarly, we found that treatment with clinically relevant drugs (e.g. quinine) led to the activation of alphaIIbbeta3 without significant changes in protein secondary structure. Molecular dynamics simulation studies revealed minor local changes in the beta-sheet probability of several extracellular domains of the integrin. Our experimental setup represents a new approach to study transmembrane proteins, especially integrins, in a membrane environment and opens a new way for testing drug binding to integrins under clinically relevant conditions.