A protein domain (grey) may have positive and negatively charged regions that generates electric force field lines that guides/orientates the positively charged peptide onto the negatively charged binding site. This allows it to dock in multiple ways on the surface of the protein via long-range and looser interactions in an encounter complex that facilitates a fast on-rate for the interaction (each peptide position is shown in a different colour). In the second step, as the correctly oriented peptide is experienced, it goes on to bind as the final complex. The encounter complex is a stable intermediate as shown in the energy diagram that describes a possible pathway from free peptide/domain to encounter to the final domain-peptide complex. See the uncovering protein structure review in this series for more information of these type of energy diagrams.