Complementary Packing of α-Helices Revisited.

The packing of α-helices in proteins is determined by both the principle of close packing and the chemical nature of side chains. As shown, amphipathic α-helices having continuous hydrophobic stripes on their surfaces can be packed against each other in two main ways referred to here as face-to-face and side-by-side manners. Three types of the minimal hydrophobic stripes produced by the heptad (7-residue), undecatad (11-residue), and 4-residue repeats in the sequence have been analyzed and their role in packing of α-helices has been considered. A variety of complementary packings of helices having minimal hydrophobic stripes have been modeled and described. This chapter presents a survey of these models as well as many examples of complementary packing of α-helices from known proteins.