Sensor histidine kinases are central to sensing in bacteria and in plants.
They usually contain sensor, linker, and kinase modules and the structure of
many of these components is known. However, it is unclear how the kinase
module is structurally regulated. Here, we use nano- to millisecond time-
resolved X-ray scattering to visualize the solution structural changes that
occur when the light-sensitive model histidine kinase YF1 is activated by blue
light. We find that the coiled coil linker and the attached histidine kinase
domains undergo a left handed rotation within microseconds. In a much slower
second step, the kinase domains rearrange internally. This structural
mechanism presents a template for signal transduction in sensor histidine
kinases