An illustration of conformational selection and population shift in protein recognition. Top: four protein conformations with different populations are shown as A, B, C, and D. The ligand may have conformation α, β, γ and δ. The mutual conformational selection between protein and ligands may generate five (roughly typical of real scenario’s) leading conformers: Aα, Bβ, Cγ, Dγ, and Dδ. The Bβ conformer has the highest population in final complex.