Fig. 5.

Knobs-into-holes (KIH) interactions. (A) A KIH interaction between two helices, seen from (i) the side and (ii) the top. The hole is shown as a solvent-accessible surface; blue indicates the surface of hydrophobic core residues, and red is a charged lysine in an e' position. The knob is donated by the right-hand helix. A Van der Waals representation of the knob is shown, and it can be seen that there is a very close steric interaction between the knob residue and the hole. (B) The hole comprises residues a', d', e', and a' (from the next helical repeat), corresponding to residues in positions i, i + 3, i + 4, and i + 7, and the knob is formed by residue a.