Quantitative Mapping of the Lipid Nanoenvironment around Transmembrane Proteins in Living Cells

TL;DR

This study explores how transmembrane proteins affect the fluidity of their surrounding lipid environment in living cells.

Contribution

The research introduces a novel method to quantify lipid nanoenvironments around transmembrane proteins in live cells.

Findings

Three of four tested transmembrane proteins do not have tightly associated boundary lipids.

The method uses mobility reduction of lipid tracers to determine protein hydrodynamic radius.

Findings challenge the role of boundary lipids as a general membrane-organizing principle.

Abstract

Weak and transient lipid–protein interactions
are thought
to shape plasma membrane organization and function but have largely
eluded experimental characterization. While model systems can only
capture certain aspects of these interactions, extraction of unambiguous
data from live cell experiments is challenging. We here ask a simple
question directed at a fundamental aspect of plasma membrane organization:
To what extent does a transmembrane protein influence, by its mere
presence, the fluidity of its immediate lipid nanoenvironment? By
specifically immobilizing proteins of interest at various densities
in the live cell plasma membrane, we were able to determine its apparent
in-plane hydrodynamic radius via quantification of the mobility reduction
of individual lipid tracer molecules. In this assay, tight adhesion
of lipid layers with reduced fluidity would manifest as an increased
effective protein radius. We compared these values with structural
biology data and used simulations to map the parameter space of possible
nanoenvironment architectures around four different transmembrane
proteins. For three of the four proteins tested, our data rule out
the presence of tightly associated boundary lipids, calling into question
their role as a general membrane-organizing principle.

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