The role of hydrophobic interactions in ankyrin-spectrin complex formation

Spectrin and ankyrin are the key components of the erythrocyte cytoskeleton. The recently published crystal structure of the spectrin-ankyrin complex has indicated that their binding involves complementary charge interactions as well as hydrophobic interactions. However, only the former is supported by biochemical evidence. We now show that nonpolar interactions are important for high affinity complex formation, excluding the possibility that the binding is exclusively mediated by association of distinctly charged surfaces. Along these lines we report that substitution of a single hydrophobic residue, F917S in ankyrin, disrupts the structure of the binding site and leads to complete loss of spectrin affinity. Finally, we present data showing that minimal ankyrin binding site in spectrin is formed by helix 14C together with the loop between helices 15 B/C.