Brief encounters of cytochrome c

Transient protein interactions are paramount to life where fast and efficient transfer of information and cargo are often integral to pathways and networks. However, complexes formed by transient protein interactions are often times resistant to direct structural characterization due to their inherent, dynamic nature, so our knowledge to date typically derives from biochemical, biophysical and computational methods. In this issue, Shimada and co‐authors present the crystal structure of the mammalian cytochrome c oxidase in complex with its electron donor cytochrome c, identifying a new class of protein–protein interaction termed “soft and specific”.