Peripheral Protein Unfolding Drives Membrane Bending

Abstract

Dynamic modulation of lipid membrane curvature can be achieved by a number of peripheral protein binding mechanisms such as hydrophobic insertion of amphipathic helices and membrane scaffolding. Recently, an alternative mechanism was proposed in which crowding of peripherally bound proteins induces membrane curvature through steric pressure generated by lateral collisions. This effect was enhanced using intrinsically disordered proteins that possess high hydrodynamic radii, prompting us to explore whether membrane bending can be triggered by the folding—unfolding transition of surface-bound proteins. We utilized histidine-tagged human serum albumin bound to Ni-NTA- DGS containing liposomes as our model system to test this hypothesis. We found that reduction of the disulfide bonds in the protein resulted in unfolding of HSA, which subsequently led to membrane tubule formation. The frequency of tubule formation was found to be significantly higher when the proteins were unfolded while being localized to a phase-separated domain as opposed to randomly distributed in fluid phase liposomes, indicating that the steric pressure generated from protein unfolding can drive membrane deformation. Our results are critical for the design of peripheral membrane protein-immobilization strategies and open new avenues for exploring mechanisms of membrane bending driven by conformational changes of peripheral membrane proteins.

The more the merrier: effects of macromolecular crowding on the structure and dynamics of biological membranes

“…4C). Similar to IDRs, unfolding of lipid‐anchored proteins could induce membrane deformations [182]. Anchoring of the folded human serum albumin to the surface of GUVs or liposomes resulted in minor membrane deformations, but enhanced tubulation was induced when the protein was chemically unfolded.…”

Site-Specific Peptide Probes Detect Buried Water in a Lipid Membrane

“…On its own, a bilayer provides a nanometer-length gradient from a polar, aqueous environment at the interface to a nonpolar hydrophobic environment within the membrane center. However, the lipid-centric view of membranes may be too simplistic because in cell membranes, transmembrane proteins make up $50% of the mass, which can significantly alter the bilayer properties (5)(6)(7). In general, residue polarity follows the hydrophilicity of its environment.…”

Strength in numbers: effect of protein crowding on the shape of cell membranes

“…In addition, a novel method to validate the effect of crowding on membrane bending is to increase the protein volume by externally triggering unfolding of domains. Siaw et al [ 41 ] demonstrated how steric pressure could be generated from chemically triggered protein unfolding, as proteins segregated into ordered lipid domains were shown to drive membrane deformation upon protein unfolding. Structural changes of integral proteins and membrane inserted domains are known to play a critical role in shaping membranes, but the work by Siaw et al shows that it is relevant to account for conformational changes in the cytosolic or ectodomains when considering crowding mechanisms.…”