Mode 3: RBD3-4 predominantly drive the interactions with a
minor contribution from RBD1-2
In this mode 3, besides the involvement of both RBD3-4 as predicted in
binding mode 1, RBD1-2 is predicted to have a minor contribution by
forming salt bridges with the phosphate backbone. This binding mode
(Fig 5 ) is only predicted with mir-21 docking scenarios.