Live cell plasma membranes do not exhibit a miscibility phase transition over a wide range of temperatures.
Lipid/cholesterol mixtures derived from cell membranes as well as their synthetic reconstitutions exhibit well-defined miscibility phase transitions and critical phenomena near physiological temperatures. This suggests that lipid/cholesterol-mediated phase separation plays a role in the organization of live cell membranes. However, macroscopic lipid-phase separation is not generally observed in cell membranes, and the degree to which properties of isolated lipid mixtures are preserved in the cell membrane remain unknown. A fundamental property of phase transitions is that the variation of tagged particle diffusion with temperature exhibits an abrupt change as the system passes through the transition, even when the two phases are distributed in a nanometer-scale emulsion. We support this using a variety of Monte Carlo and atomistic simulations on model lipid membrane systems. However, temperature-dependent fluorescence correlation spectroscopy of labeled lipids and membrane-anchored proteins in live cell membranes shows a consistently smooth increase in the diffusion coefficient as a function of temperature. We find no evidence of a discrete miscibility phase transition throughout a wide range of temperatures: 14-37 °C. This contrasts the behavior of giant plasma membrane vesicles (GPMVs) blebbed from the same cells, which do exhibit phase transitions and macroscopic phase separation. Fluorescence lifetime analysis of a DiI probe in both cases reveals a significant environmental difference between the live cell and the GPMV. Taken together, these data suggest the live cell membrane may avoid the miscibility phase transition inherent to its lipid constituents by actively regulating physical parameters, such as tension, in the membrane.
†Department of Chemistry, California Institute for Quantitative Biosciences (QB3), Howard Hughes Medical Institute, University of California, Berkeley, California 94720, United States.
Il-Hyung
IH
Lee
§National Centre for Biological Sciences (TIFR), Bellary Road, Bangalore 560065, India.
Suvrajit
S
Saha
∥Raman Research Institute, C.V. Raman Avenue, Bangalore 560080, India.
Anirban
A
Polley
†Department of Chemistry, California Institute for Quantitative Biosciences (QB3), Howard Hughes Medical Institute, University of California, Berkeley, California 94720, United States.
Hector
H
Huang
§National Centre for Biological Sciences (TIFR), Bellary Road, Bangalore 560065, India.
Satyajit
S
Mayor
§National Centre for Biological Sciences (TIFR), Bellary Road, Bangalore 560065, India.|∥Raman Research Institute, C.V. Raman Avenue, Bangalore 560080, India.
Madan
M
Rao
†Department of Chemistry, California Institute for Quantitative Biosciences (QB3), Howard Hughes Medical Institute, University of California, Berkeley, California 94720, United States.|‡Materials Sciences Division, Physical Biosciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States.
Jay T
JT
Groves
D002462:Cell Membrane / Q000737:chemistry*; D004058:Diffusion; D006801:Humans; D019169:Jurkat Cells; D008563:Membrane Lipids / Q000737:chemistry; D008567:Membranes, Artificial; D008954:Models, Biological; D056004:Molecular Dynamics Simulation; D009010:Monte Carlo Method; D044367:Phase Transition; D013050:Spectrometry, Fluorescence; D013696:Temperature
D008563:Membrane Lipids; D008567:Membranes, Artificial