A Biophysical Investigation of the Duality in Fas Receptor

Membrane receptors control fundamental physiological processes in cells, and are major targets of medical drugs.

The goal of this project is to investigate the nanoscale motion of the membrane receptor Fas and its functional role in maintaining immune surveillance. Fas is ubiquitously expressed in human body and has significant roles in disease progressions.

A type I single pass transmembrane protein, Fas is known for its ‘dual character’ in triggering signaling pathways leading to both cell survival and cell death.

In the presence of its ligand, the receptor undergoes higher-order clustering to form a death-inducing signaling complex (DISC) in the intracellular region. Immune cells use Fas-mediated DISC formation as a mechanism to ‘kill’ virus infected or malignant cells. The Fas ligand, which is a type II transmembrane protein, can be cleaved which results in its soluble variant.

Unlike the membrane anchored Fas ligand, the cleaved variant is known to induce an alternative motility inducing signaling complex (MISC) in Fas receptor that results in cell migration.

Although the functions of the Fas receptor (and the notion of duality) are well established, how it selects for non-apoptotic or apoptotic pathways is an open question.

It has been postulated that the membrane bound and cleaved variants of the Fas ligand induce different structural orientation and conformations in the intracellular domains of the receptors to control DISC/MISC formation.

However, due to the immediate higher order aggregations upon ligand-binding and the presence of other modulating proteins during in-vivo experiments, it has been a great challenge to test this hypothesis.

This project will investigate the biophysical mechanism behind the duality in full-length Fas receptors by exploiting single-molecule Förster resonance energy transfer (smFRET) and membrane nanodisc platform. Mechanistic understanding of Fas transmembrane signaling has both scientific and pharmaceutical significance.