  Protein dynamics is a fundamental element to comprehend their biological
functions. However, a theoretical picture providing microscopic-detail
explanation of its relevant features is still missing. One of the outmost
relevant properties exhibited by this dynamic is its subdiffusivity, whose
origins are still unknown. Here, by directly comparing all-atom molecular
dynamics simulations and theory we show that this behavior mainly arises from
the fractal nature of the network of metastable state of conformational state
over which protein dynamics, thought as diffusion process, takes place. This
process is assumed to be Markovian by the employed theoretical picture.
Therefore, to further support its validity, we built a simple Markov state
model starting from the simulations outcome and show that it exhibits a
subdiffusive behavior, in quantitative agreement with the one associated to the
molecular dynamics. Moreover, Molecular dynamics gives direct access to
relevant quantities which allowed us to rule out the possibility the Continuous
Time Random Walk can explain the protein subdiffusivity.
