How are the α-helices in α-keratin connected to each other?

The α-helices in α-keratin are primarily connected to each other by disulfide bonds. These disulfide bonds are covalent linkages formed between the sulfur atoms of cysteine residues on different helices. This connection is crucial for stabilizing the structural integrity of the keratin protein, allowing it to withstand mechanical stress.

Keratin exists in various forms, such as hair, nails, and horns, and the presence of these disulfide bridges contributes significantly to the hardness and resilience of these structures. While hydrogen bonds also play a role in stabilizing the α-helical structure itself, the primary inter-chain connections in α-keratin that contribute to its overall strength and durability come from these disulfide bonds.

Peptide bonds are responsible for linking amino acids together to form the polypeptide chain, while ionic bonds are generally less significant in the stabilizing structure of keratin compared to the prominent role of disulfide bonds.