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Directed manipulation of membrane proteins by fluorescent magnetic nanoparticles

Jia Hui Li, Paula Santos-Otte, Braedyn Au, Jakob Rentsch, Stephan Block, Helge Ewers

Preprint posted on 1 April 2020 https://www.biorxiv.org/content/10.1101/2020.03.30.016477v1

Article now published in Biophysical Journal at http://dx.doi.org/10.1016/j.bpj.2019.11.1764

Magnetic fields and single-molecule manipulation in live cells.

Selected by Mariana De Niz

Background

The plasma membrane is the interface through which cells interact with their environment. Membrane proteins are heterogeneously distributed in the plasma membrane of cells despite the membrane’s fluid and continuous nature. The function of membrane proteins in the context of the lipid bilayer of the plasma membrane, is linked to the specific location within the membrane and their dynamics. Such location is crucial for the execution and regulation of fundamental biological processes. Multiple imaging techniques have aided in the description of the local membrane composition and dynamics. Although perturbation of the function, localization and dynamics of membrane molecules has been achieved through the use of genetic or pharmacological means, this usually leads to global effects and limited temporal resolution. Methods that allow manipulation of membrane protein localization at the single molecule level have been lacking. In their present work, Li et al used fluorescent magnetic nanoparticles (FMNPs) to track membrane molecules, and manipulate their movement, at a high temporal and spatial resolution (1).

Figure 1. Directed manipulation of membrane proteins by fluorescent magnetic nanoparticles. (From ref 1).

 

Key findings and developments

Recent advances in the use of biofunctionalized magnetic particles to remotely control cellular processes have opened a new field termed “magnetogenetics”. In the case of the plasma membrane, various receptors and/or ion channels can be activated using magnetic particles. In their work, Li at al use FMNPs sized below the diffraction limit of light to retrieve information on single molecules with high spatiotemporal resolution. They used particles with a 100nm diameter ferromagnetic core, and a polymer shell conjugated with a fluorescent dye and streptavidin. The magnetic component of the particles allows manipulation through applying an external magnetic field, allowing to pool membrane components laterally through the membrane with femtonewton-range forces. A magnetized needle allowed dragging lipid-anchored and transmembrane proteins over the surface of living cells, while upon removal of the needle, the particles returned to random motion – showing that particle manipulation was reversible and temporally controlled.

The authors determined that single particle tracking at 10nm spatial, and 5ms temporal resolution in up to 10,000 frames, was possible. They also showed that the system could be applied to living cells, by coupling FMNPs to commonly studied plasma membrane proteins with different anchoring moieties. The nanobody-conjugated FMNPs bound on the dorsal membrane of transfected cells could be readily tracked and manipulated. Moreover, the authors went on to investigate whether the motion of membrane proteins could be correlated with the location of cellular structures, such as the cortical cytoskeleton. They found that their system allows studying molecule dynamics upon experiencing a physical barrier imposed by structures such as actin filaments, actin-associated transmembrane proteins, extracellular matrix, or cellular structures (eg. clathrin-coated pits). Altogether the authors present their system as a novel tool to study membrane protein location in a dynamic manner, and the interaction of such proteins with cellular events and structures.

What I like about this preprint

I like out-of-the box thinking and interdisciplinary approached in research, including the application to biological questions. I find this preprint does this, and bring forward an exciting tool to study membrane dynamics at a single molecule level, and interactions of membrane proteins with cellular structures. I think this is an exciting advance in cell biology per se, and applicable to various broader fields of research.

Open questions

  1. How do you ensure that through magnetic manipulation you do not alter the function of the molecules studied?
  1. Can you use FMNPs in combination with other imaging techniques to visualize dynamic events happening at the physical barriers you describe – eg.actin filaments, etc.
  1. Is it possible, using FMNPs to manipulate an entire group of proteins – for instance the actin cytoskeleton, in specific ways, to observe how other proteins behave in this environment? Is it possible to use FMNPs in combination with pharmacological or genetic tools too?
  1. Can you expand further on how you define the number and size of FMNPs used per cell, optimal for single molecule studies?
  1. Beyond manipulation of single molecules, as a bigger picture, can you use FMNPs to simulate conditions of cellular stress specific to particular diseases?
  1. You used in this study, FMNPs to study membrane proteins. Do you envisage using this to study for instance, specific proteins in organelles such as the Golgi, the ER or the mitochondria? This would open an extremely exciting new world in cell biology…
  1. Can you use different magnetic force to manipulate different sets of molecules simultaneously (equivalent of using fluorophores of different wavelengths for simultaneous visualization)?

References

  1. Jia Hui Li, et al , Directed manipulation of membrane proteins by fluorescent magnetic nanoparticles, bioRxiv, 2020.

 

 

Posted on: 26 April 2020 , updated on: 27 April 2020

doi: https://doi.org/10.1242/prelights.19350

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