A model for ribosome translocation based on the alternated displacement of its subunits

A meaningful dilemma in ribosome translocation arising from experimental facts is that, although the ribosome-mRNA interaction force always has a significant magnitude, the ribosome still moves to the next codon on the mRNA. How does the ribosome manage to move to the next codon in the sequence while holding the mRNA tightly? The hypothesis proposed here is that ribosome subunits alternate the grip of the ribosome on the mRNA to allow the other subunit to be free of such interaction for a while, thus moving to the following codon in the chain. Based on this assumption, a single-loop cycle of ribosome configurations involving the relative position of its subunits is elaborated and, when its dynamics is modeled as a Markov network, gives expressions for the average ribosome translocation speed and stall force as functions of the equilibrium constants among the ribosome configurations. The calculations show a reasonable agreement with experimental results, and the succession of molecular events considered here is consistent with current biomolecular concepts of the ribosome translocation process. The above shows the feasibility of the alternated displacements hypothesis proposed in this work to explain ribosome translocation.