  Proteins are large and complex molecular machines. In order to perform their
function, most of them need energy, e.g. either in the form of a photon, like
in the case of the visual pigment rhodopsin, or through the breaking of a
chemical bond, as in the presence of adenosine triphosphate (ATP). Such energy,
in turn, has to be transmitted to specific locations, often several tens of
Angstroms away from where it is initially released. Here we show, within the
framework of a coarse-grained nonlinear network model, that energy in a protein
can jump from site to site with high yields, covering in many instances
remarkably large distances. Following single-site excitations, few specific
sites are targeted, systematically within the stiffest regions. Such energy
transfers mark the spontaneous formation of a localized mode of nonlinear
origin at the destination site, which acts as an efficient energy-accumulating
centre. Interestingly, yields are found to be optimum for excitation energies
in the range of biologically relevant ones.
