The differences between the native state and alternative competing states can generally be attributed to the amino acid composition of each sequence (Table ). In the case of CC-Di, each monomer has an Asn residue at the a position of one of its central heptads, which strongly favours the parallel dimer state due to the formation of interhelical Asn-Asn hydrogen bonds. Notably, substitution of Asn to Ile, which is ordinarily present at the a position in coiled-coil dimers (and is present in all other a positions of the CC-Di sequence), results in a parallel trimer instead; 33 therefore, the presence of the Asn residues confers high selectivity for the parallel dimer state. It has been proposed that, in the dimer state, the cost of burying two Asn residues at the hydrophobic peptide core is offset by the formation of the intermolecular hydrogen bond. However, the burial of more than two Asn residues is not tolerated in higher oligomerisation states, rendering the trimer and tetramer states less favourable. The more Asn residues are attempted to be buried at the hydrophobic core, the less stable the assembly, hence the ∆G • bind,total /helix for the tetrameric CC-Di being less favourable than that of the trimeric CC-Di (Figure ).