  Protein$\alpha$-helices provide an ordered biological environment that is
conducive to soliton-assisted energy transport. The nonlinear interaction
between amide I excitons and phonon deformations induced in the hydrogen-bonded
lattice of peptide groups leads to self-trapping of the amide I energy, thereby
creating a localized quasiparticle (soliton) that persists at zero temperature.
The presence of thermal noise, however, could destabilize the protein soliton
and dissipate its energy within a finite lifetime. In this work, we have
computationally solved the system of stochastic differential equations that
govern the quantum dynamics of protein solitons at physiological temperature,
T=310 K, for either a single isolated $\alpha$-helix spine of hydrogen bonded
peptide groups or the full protein $\alpha$-helix comprised of three parallel
$\alpha$-helix spines. The simulated stochastic dynamics revealed that although
the thermal noise is detrimental for the single isolated $\alpha$-helix spine,
the cooperative action of three amide I exciton quanta in the full protein
$\alpha$-helix ensures soliton lifetime of over 30 ps, during which the amide I
energy could be transported along the entire extent of an 18-nm-long
$\alpha$-helix. Thus, macromolecular protein complexes, which are built up of
protein $\alpha$-helices could harness soliton-assisted energy transport at
physiological temperature. Because the hydrolysis of a single adenosine
triphosphate molecule is able to initiate three amide I exciton quanta, it is
feasible that multiquantal protein solitons subserve a variety of specialized
physiological functions in living systems.
