Abstract
The cell membrane plays a key role in compartmentalization, nutrient transportation and signal transduction, while the pattern of protein distribution at both cytoplasmic and ectoplasmic sides of the cell membrane remains elusive. Using a combination of single-molecule techniques, including atomic force microscopy (AFM), single molecule force spectroscopy (SMFS) and stochastic optical reconstruction microscopy (STORM), to study the structure of nucleated cell membranes, we found that (1) proteins at the ectoplasmic side of the cell membrane form a dense protein layer (4 nm) on top of a lipid bilayer; (2) proteins aggregate to form islands evenly dispersed at the cytoplasmic side of the cell membrane with a height of about 10–12 nm; (3) cholesterol-enriched domains exist within the cell membrane; (4) carbohydrates stay in microdomains at the ectoplasmic side; and (5) exposed amino groups are asymmetrically distributed on both sides. Based on these observations, we proposed a Protein Layer-Lipid-Protein Island (PLLPI) model, to provide a better understanding of cell membrane structure, membrane trafficking and viral fusion mechanisms.
Highlights
The cell membrane, termed the plasma membrane, plays a crucial role in various cellular activities, such as signal transduction, membrane trafficking, as well as energy conversion [1,2,3,4]
In order to verify the feature of the native cell membrane, we directly imaged the ectoplasmic surface of living cells
We previously decorated antibodies on the cell membranes, and the result showed that the resolution of atomic force microscopy (AFM) was high enough to distinguish protruding proteins from the surface of cell membranes [32]
Summary
The cell membrane, termed the plasma membrane, plays a crucial role in various cellular activities, such as signal transduction, membrane trafficking, as well as energy conversion [1,2,3,4]. Different cell membrane models have been introduced over the past century, we are still far from fully understanding this important cellular component [5,6,7]. The structure of the cell membrane was initially viewed as a sandwich that consists of protein-lipid-protein [8]. With the realization of dynamic protein distribution in the cell membrane, the fluid mosaic model was introduced and has become the most accepted model until now. The fluid mosaic model highlights the aspects of ‘‘diffusion’’ and ‘‘mosaicism’’, emphasizing that 1) both lipids and proteins are dynamic and diffuse randomly in the homogeneous lipid bilayer and 2) proteins are asymmetrically distributed in the cell membrane [5]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
