RESUMEN
Temperature is a critical parameter for biological function, yet there is a lack of approaches to modulate the temperature of biological specimens in a dynamic and high-throughput manner. We present the thermoPlate, a device for programmable control of temperature in each well of a 96-well plate, in a manner compatible with mammalian cell culture and live cell imaging. The thermoPlate maintains precise feedback control of temperature patterns independently in each well, with minutes-scale heating and cooling through ΔT ~15-20°C. A computational model that predicts thermal diffusion guides optimal design of heating protocols. The thermoPlate allowed systematic characterization of both synthetic and natural thermo-responsive systems. We first used the thermoPlate in conjunction with live-cell microscopy to characterize the rapid temperature-dependent phase separation of a synthetic elastin-like polypeptide (ELP53). We then measured stress granule (SG) formation in response to heat stress, observing differences in SG dynamics with each increasing degree of stress. We observed adaptive formation of SGs, whereby SGs formed but then dissolved in response to persistent heat stress (≥ 42°C). SG adaptation revealed a biochemical memory of stress that depended on both the time and temperature of heat shock. Stress memories continued to form even after the removal of heat and persisted for 6-9 hours before dissipating. The capabilities and open-source nature of the thermoPlate will empower the study and engineering of a wide range of thermoresponsive phenomena.
RESUMEN
Inducible protein switches are used throughout the biosciences to allow on-demand control of proteins in response to chemical or optical inputs. However, these inducers either cannot be controlled with precision in space and time or cannot be applied in optically dense settings, limiting their application in tissues and organisms. Here we introduce a protein module whose active state can be reversibly toggled with a small change in temperature, a stimulus that is both penetrant and dynamic. This protein, called Melt (Membrane localization through temperature), exists as a monomer in the cytoplasm at elevated temperatures but both oligomerizes and translocates to the plasma membrane when temperature is lowered. Using custom devices for rapid and high-throughput temperature control during live-cell microscopy, we find that the original Melt variant fully switches states between 28-32°C, and state changes can be observed within minutes of temperature changes. Melt was highly modular, permitting thermal control over diverse intracellular processes including signaling, proteolysis, and nuclear shuttling through straightforward end-to-end fusions with no further engineering. Melt was also highly tunable, giving rise to a library of Melt variants with switch point temperatures ranging from 30-40°C. The variants with higher switch points allowed control of molecular circuits between 37°C-41°C, a well-tolerated range for mammalian cells. Finally, Melt could thermally regulate important cell decisions over this range, including cytoskeletal rearrangement and apoptosis. Thus Melt represents a versatile thermogenetic module that provides straightforward, temperature-based, real-time control of mammalian cells with broad potential for biotechnology and biomedicine.
RESUMEN
Protein clustering is a powerful form of optogenetic control, yet remarkably few proteins are known to oligomerize with light. Recently, the photoreceptor BcLOV4 was found to form protein clusters in mammalian cells in response to blue light, although clustering coincided with its translocation to the plasma membrane, potentially constraining its application as an optogenetic clustering module. Herein we identify key amino acids that couple BcLOV4 clustering to membrane binding, allowing us to engineer a variant that clusters in the cytoplasm and does not associate with the membrane in response to blue light. This variant-called BcLOVclust-clustered over many cycles with substantially faster clustering and de-clustering kinetics compared to the widely used optogenetic clustering protein Cry2. The magnitude of clustering could be strengthened by appending an intrinsically disordered region from the fused in sarcoma (FUS) protein, or by selecting the appropriate fluorescent protein to which it was fused. Like wt BcLOV4, BcLOVclust activity was sensitive to temperature: light-induced clusters spontaneously dissolved at a rate that increased with temperature despite constant illumination. At low temperatures, BcLOVclust and Cry2 could be multiplexed in the same cells, allowing light control of independent protein condensates. BcLOVclust could also be applied to control signaling proteins and stress granules in mammalian cells. While its usage is currently best suited in cells and organisms that can be cultured below â¼30 °C, a deeper understanding of BcLOVclust thermal response will further enable its use at physiological mammalian temperatures.
