Person:

Stossel, Thomas

The actin crosslinking protein filamin A (FLNa) mediates mechanotransduction, a conversion of mechanical forces into cellular biochemical signals to regulate cell growth and survival. To provide more quantitative insight into this process, we report results using magnetic tweezers that relate mechanical force to conformational changes of FLNa immunoglobulin-like repeats (IgFLNa) 20–21, previously identified as a mechanosensing domain. We determined the force magnitudes required to unfold previously identified structural organizations of the β-strands in the two domains: IgFLNa 20 unfolds at ~15 pN and IgFLNa 21 unfolding requires significantly larger forces. Unfolded domain IgFLNa 20 can exist in two different conformational states, which lead to different refolding kinetics of the IgFLNa 20 and imply a significant impact on the reformation of the domain pair at reduced force values. We discuss the relevance of the findings to force bearing and mechanosensing functions of FLNa.

Endogenously and externally generated mechanical forces influence diverse cellular activities, a phenomenon defined as mechanotransduction. Deformation of protein domains by application of stress, previously documented to alter macromolecular interactions in vitro, could mediate these effects. We engineered a photon-emitting system responsive to unfolding of two repeat domains of the actin filament (F-actin) crosslinker protein filamin A (FLNA) that binds multiple partners involved in cell signaling reactions and validated the system using F-actin networks subjected to myosin-based contraction. Expressed in cultured cells, the sensor-containing FLNA construct reproducibly reported FLNA domain unfolding strikingly localized to dynamic, actively protruding, leading cell edges. The unfolding signal depends upon coherence of F-actin-FLNA networks and is enhanced by stimulating cell contractility. The results establish protein domain distortion as a bona fide mechanism for mechanotransduction in vivo.

Despite the growth of research in universities on point-of-care (POC) diagnostics for global health, most devices never leave the laboratory. The processes that move diagnostic technology from the laboratory to the field—the processes intended to evaluate operation and performance under realistic conditions—are more complicated than they might seem. Two case studies illustrate this process: the development of a paper-based device to measure liver function, and the development of a device to identify sickle cell disease based on aqueous multiphase systems (AMPS) and differences in the densities of normal and sickled cells. Details of developing these devices provide strategies for forming partnerships, prototyping devices, designing studies, and evaluating POC diagnostics. Technical and procedural lessons drawn from these experiences may be useful to those designing diagnostic tests for developing countries, and more generally, technologies for use in resource-limited environments.