On the stability and plastic properties of the interior L3 loop in R. capsulatus porin. A molecular dynamics study.

Structural properties of Rhodobacter capsulatus porin are studied by molecular dynamics simulation using the GROMOS force field. Unconstrained simulations of the trimer and monomer show the trimer to be more stable than the isolated monomer. Simulations of the L3 loop inside the pore are used to assess its stability and plastic properties. Simulated annealing shows that the conformational space available to the L3 loop inside the pore is very large. Simulations at different temperatures show that the energy hypersurface around the open state is complex and flat. These studies also indicate four zones that are more flexible than the rest of the loop. Two of these are stabilized by the addition of the detergent molecule present in the X-ray structure. It is possible that the two remaining flexible zones, situated in the half of the loop facing the extracellular end of the porin molecule, residues Asp93-Gly98 and Arg110-Leu111, are involved in a mechanism for opening and closing of the pore.