Figure 2

Topology diagram of a single ligand domain associated with high- and low-affinity receptors. β-strands of the receptor molecules are shown as arrows and the helices are shown as rectangles. Binding loops of the receptor D1 domain are red and the loops of the D2 domain are blue. α-helices of single ligand domain are shown as circles. Helices A, B, C, and D (red) belong to one polypeptide chain of the ligand and helices E' and F' (green) belong to another polypeptide chain of the ligand. Highlighted helices (A, C, D, F') constitute the four-helix bundle that is involved in receptor binding.