Illustration of cation-pi connections in a protein from the marine bacterium Mycobacterium marinum. Tryptophan aromatic rings (yellow surfaces) are interacting with positive areas in the arginine side chains (orange surfaces) to stabilise the folding of the monomer protein and also to connect them to form the final dimer (molecule made from two identical monomer subunits). The inter-amino acid interactions are based on cation-pi connections.