Lipid Rafts: Buffers of Cell Membrane Physical Properties

Abstract

Lateral organization of lipids in the cell membrane appears to be an ancient feature of the cell, given the existence of lipid rafts in both eukaryotic and prokaryotic cells. Currently seen as platforms for protein partitioning, we posit that lipid rafts are capable of playing another role: stabilizing membrane physical properties over varying temperatures and other environmental conditions. Membrane composition defines the mechanical and viscous properties of the bilayer. The composition also varies strongly with temperature, with systematic changes in the partitioning of high and low melting temperature membrane components. In this way, rafts function as buffers of membrane physical properties, progressively counteracting environmental changes via compositional changes; i.e., more high melting lipids partition to the fluid phase with increasing temperature, increasing the bending modulus and viscosity, as thermal effects decrease these same properties. To provide an example of this phenomenon, we have performed neutron scattering experiments and atomistic molecular dynamics simulations on a phase separated model membrane. The results demonstrate a buffering effect in both the lateral diffusion coefficient and the bending modulus of the fluid phase upon changing temperature. This demonstration highlights the potentially advantageous stabilizing effect of complex lipid compositions in response to temperature and potentially other membrane destabilizing environmental conditions.

High-resolution neutron spectroscopy using backscattering and neutron spin-echo spectrometers in soft and hard condensed matter

“…Furthermore, new insight into the role of rafts was obtained through NSE measurements of the lateral diffusion coefficients in a phase-separated lipid mixture. In agreement with structural and dynamical data from molecular dynamics simulations, the measurements indicate that rafts function as buffers of membrane properties and that a change in the complex lipid compositions in response to a variation in external parameters (such as temperature) may provide an advantageous stabilizing effect 71 .…”

The Diapause Lipidomes of Three Closely Related Beetle Species Reveal Mechanisms for Tolerating Energetic and Cold Stress in High-Latitude Seasonal Environments

“…The various ways of biochemical acclimatization of lipid structures to maintain functionality as temperature decreases are often gathered under the umbrella term HVA, which include the HPA and the DPB theory (Sinensky, 1974;Lewis et al, 1989;Hazel, 1995). Central to all is the temperature-dependent dynamism in the lipid bilayer (Zehmer, 2005;Nickels et al, 2019). It should be stressed that there are several mechanisms by which proper lipid composition and physical properties are maintained, and that no clear taxonomic patterns exist, i.e., some animal groups employing only a certain acclimatization response (Koštál, 2010).…”

Impact of Fatty-Acid Labeling of Bacillus subtilis Membranes on the Cellular Lipidome and Proteome

“…This hypothesis provides a compelling rationale for numerous observations relating to membrane trafficking, endocytosis, signal transduction, and other processes (Simons and Toomre, 2000;Simons and Ehehalt, 2002;Shaw, 2006;Allen et al, 2007). It has also been suggested that rafts may contribute to the short-term physical stability of the cell membrane by buffering the mechanical properties of the membrane against rapid changes in temperature, local solvents, and other environmental perturbations (Nickels et al, 2019). Experimental evidence describing lipid rafts has been largely inferential due to the limitations of traditional techniques, and it is widely believed that these features are nanoscopic, as well as transient (Mukherjee and Maxfield, 2004;Lingwood and Simons, 2010), making them difficult to detect in vivo.…”