Actomyosin fibers in non-muscle cells generate contractile force to drive cell morphogenesis and migration. We find another role of these fibers as a platform for generating force-dependent biochemical signals. The MAP kinase ERK is activated on actomyosin fibers in response to tension developed in the fibers, which contributes to detecting anisotropy of cell deformation. The actin-binding, myosin-modulating protein calponin-3 is also phosphorylated on actomyosin fibers dependently on the fiber tension, which in turn increases myosin-based contractile force generation in the fibers. This positive feedback mechanism for tension development in actomyosin fibers enhances generation of force-dependent biochemical signals on the fibers.
Within a thermally fluctuating protein molecule under physiological conditions, tightly packed amino acid residues interact with each other through energy and heat exchanges. We have developed a computer program CURP (CURrent calculation for Proteins), which is suitable for analyzing non-uniform flow of heat and energy in proteins. We illustrate and characterize non-uniform pattern of energy flow in proteins with the energy exchange network (EEN) model based on the transport coefficient of energy flow between each residue pair. EEN diagrams demonstrated characteristic features of “hidden dynamic allostery” in PDZ domain and allosteric transition in the oxygen sensor domain of FixL.
Temperate plants enhance their freezing tolerance before winter to survive in freezing environment. Plants use the cytosolic transient Ca2+ concentration change as a kind of signal to regulate gene expression in cold acclimation process. We developed the experimental system for observation of Ca2+ signal during cooling, and observed Ca2+ signal to understand “how plants sense cold and seasonal changes.” We found several characteristics of Ca2+ signal and cold sensing. For example, plants adjust the Ca2+ signal to the ambient temperature to response small temperature decrease, and then small temperature fluctuation induces the cold-inducive transcription factor DREB1/CBFs expression via Ca2+ signals.