Tunable molecular tension sensors reveal extension-based control of vinculin loading

Andrew S LaCroix, Andrew D Lynch, Matthew E Berginski, Brenton D Hoffman

Posted on: 4 March 2018

Preprint posted on 12 February 2018

Article now published in eLife at http://dx.doi.org/10.7554/elife.33927

The tension sensors of the future - better optimized genetically encoded probes reveal novel mechanistic detail in how mechanotransduction works

Selected by Amanda Haage

Categories: biophysics, cell biology

Why This Is Cool – It is now widely accepted that besides responding to chemical cues in their environment, cells also participate in mechanotransduction, a process by which they sense and respond to physical aspects of the environment (i.e. matrix stiffness or shear stress, etc.). The main way cells do this is through mechanosensitive signaling or the conformational change of load-bearing proteins in response to force. The main way this has been studied is through FRET-based tension sensors that are genetically encoded into those load-bearing proteins. The problem addressed by this work is that to date, the design of these tension sensors has been based on models created in cell-free systems, but they are then exclusively used in cells. Here they provide a novel and validated method for predicting tension sensor sensitivity in cells. This allows them to create an optimized tension sensor for the load-bearing protein vinculin that is determined to be 300% better by their calculations. They use this optimized sensor to demonstrate a gradient of forces across focal adhesions at the cell periphery. They are also able to use sensors of varying length to determine that protein extension, rather than the force experienced by the protein, may be the major mechanism of mechanical signaling in cells. This work provides an incredibly useful tool in mapping out the future of precise new sensor design. It demonstrates the usefulness of optimized sensors to uncover new mechanisms of mechanical signaling.

Fig. 1 – (A) Design and characterization of tunable FRET-based molecular tension sensors. Sensor function depends on the Förster radius of the chosen FRET pair (B) as well as the length (C) and stiffness (D) of the extensible polypeptide domain.

Why I Selected It – I think the model presented here will quickly be adopted as the new standard in molecular tension sensor design. They have essentially eliminated the previous system of designing that was based on literature guesswork and then checking if sensors work through extensive cellular characterization. As someone interested in mechanobiology, I look forward to seeing a new crop of tension sensors that are designed based on this model and expanded to other load-bearing proteins.

Open Questions –

Are there any reasons the principles of tension sensor design discussed here could not be expanded to proteins other than vinculin?
In which cellular contexts would either an extension- or force-based control mechanism be more advantageous? Why would this be a context-specific way to modulate mechanical signaling?
Will tension sensors ever be useful in vivo?

Related Research –

The first calibrated genetically-encoded molecular tension sensor module & the original vinculin tension sensor
- Grashoff, C., Hoffman, B. D., Brenner, M. D., Zhou, R., Parsons, M., Yang, M. T., McLean, M. A., Sligar, S. G., Chen, C. S., Ha, T., Schwartz, M. A. (2010). Measuring mechanical tension across vinculin reveals regulation of focal adhesion dynamics. Nature, 466: 263-266. doi:10.1038/nature09198
Review of the field and current limitations
- Freikamp, A., Mehlich, A., Klingner, C., Grashoff, C. (2016b). Investigating piconewton forces in cells by FRET-based molecular force microscopy. J Struct Biol. doi:10.1016/j.jsb.2016.03.011

Tags: cell-ecm adhesion, mechanotransduction, protein biology

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Author's response

Brent Hoffman shared

The new modules can be applied to any existing tension sensor. There are always challenges associated with making a tension sensor for a new protein, as a significant number of controls have to be done to ensure that the insertion of the tension sensing module does not affect the function of the protein to be studied. In this regard, the modules developed in this work have all the same issues as the other published modules.
Great question. We are working on it now
While not our work, there are several examples of the tension sensor being useful in vivo. Here are two examples. Some of the papers are quite recent.
1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4118667/. Although this study has recently been challenged: https://www.nature.com/articles/s41598-017-14136-y
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5680264/