  We report on charge transport and current fluctuations in a single
bacteriorhodpsin protein in a wide range of applied voltages covering direct
and injection tunnelling regimes. The satisfactory agreement between theory and
available experiments validates the physical plausibility of the model
developed here. In particular, we predict a rather abrupt increase of the
variance of current fluctuations in concomitance with that of the I-V
characteristic. The sharp increase, for about five orders of magnitude of
current variance is associated with the opening of low resistance paths
responsible for the sharp increase of the I-V characteristics. A strong
non-Gaussian behavior of the associated probability distribution function is
further detected by numerical calculations.
