Protein passage across live cell membranes
The speed with which proteins move within a cell profoundly affects their biological function, take for example, reaction rates. The D_IN_VIVO (A general law describing the diffusion of membrane proteins in vivo based on single molecule tracking of membrane proteins in Escherichia coli) project has designed and developed methods to measure the effect of viscosity of membranes Initially, D_IN_VIVO researchers worked on the rate of diffusion of proteins, taking into account the space proteins occupy in the membrane. However, on discovery of another almost identical research project underway, D_IN_VIVO decided to investigate the impact of membrane viscosity on speed of protein movement, a feature never before investigated. In common with the previous research, the rate of diffusion is based on the Saffman-Delbrueck (SD) model. Moreover, the methods involve skills in single molecule tracking, programming and how to build/align microscope set-ups. Instead of the fluorescent protein mEos2, D_IN_VIVO used PamCherry to overcome blinking behaviour. Using molecular rotors developed in another lab in Imperial College, London, the researchers determined the viscosity of live E. coli plasma membranes, spheroplasts and vesicles made of the bacterium’s lipid extracts. They found that fluorescence emissions depend on viscosity in molecular rotors. Research results showed a high viscosity, higher than in other live cell membranes such as eukaryotic and Bacillus vegetative cells, suggesting a high degree of lipid ordering within the liquid-phase membrane. The viscosity matched well with the results obtained by the other group using the SD model. The results were published in an article in the Biophysical Journal. Viscosity is a highly important parameter within the plasma membrane, controlling the rate of diffusion of small molecules and proteins. As such, the project research has delivered important data that could be used for estimating drug delivery and rates of intracellular reactions.
Keywords
Protein, live cell membranes, diffusion, D_IN_VIVO, viscosity
