https://doi.org/10.1140/epje/s10189-023-00372-w
Regular Article - Living Systems
MFG-E8: a model of multiple binding modes associated with ps-binding proteins
1
Department of Chemistry, The University of Chicago, Chicago, IL, USA
2
Program in Biophysical Sciences, Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL, USA
3
James Franck Institute, The University of Chicago, Chicago, IL, USA
4
Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA
5
NSF’s ChemMatCARS, The University of Chicago, Chicago, IL, USA
Received:
12
June
2023
Accepted:
18
October
2023
Published online:
24
November
2023
Membrane-binding proteins often associate with lipid membranes through a singular binding interface which is generally modeled as a two-state system: bound or unbound. However, even a single interface can engage with more than one mode of binding since a variety of interactions can contribute to the binding event. Unfortunately, the ability to clearly delineate the different binding modes of a singular binding interface has been elusive with existing models. Here, we present a study on milk fat globule EGF factor 8 (MFG-E8), which belongs to a class of proteins that identifies and binds phosphatidylserine (PS). These proteins detect membrane dysregulation implicated in exposed PS in apoptosis and malignant cells. In order to elucidate the factors affecting the binding of MFG-E8, we used a model system consisting of a series of lipid vesicles with varying PS mole fraction to identify the sensitivity of MFG-E8’s binding affinity to changes in electrostatics using a tryptophan fluorescence spectral shift assay. Using a newly developed model, we experimentally identified three binding modes, each associated with a different number of PS lipids, with its cooperativity for binding being enhanced by the availability of negatively charged lipids. X-ray reflectivity experiments additionally suggest that MFG-E8’s binding modes are influenced by membrane packing. The protocols established for elucidating MFG-E8’s interaction with lipid membranes under different membrane conditions can be applied to the study of other membrane-binding proteins that target specific membrane attributes, such as fluidity and electrostatics, and help elucidate these membrane targeting mechanisms and their subsequent binding events.
This article is dedicated to Fyl Pincus who has made many important contributions to soft matter and biological physics. His scientific achievements, insights and mentoring have inspired and enriched many, and have made a lasting impact on our community.
Supplementary Information The online version contains supplementary material available at https://doi.org/10.1140/epje/s10189-023-00372-w.
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© The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature 2023. Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
