What is the average distance between backbones in an α-helix?

The average distance between backbones in an α-helix is approximately 5.4 Å. In an α-helix, the backbone represents the repeating structure formed by the peptide bonds of amino acids. Each turn of the helix typically contains about 3.6 amino acids, leading to a rise of around 1.5 Å per residue vertically along the helical axis.

When calculating the distance from one backbone to the next, the helical structure's geometry allows for the close packing of atoms, which results in the characteristic distance of about 5.4 Å between successive backbone carbonyl (C=O) oxygen atoms. This distance contributes to the overall stability and compactness of the α-helix conformation, influencing protein folding and function.

Understanding this structural feature is essential for studying protein architecture, as the orientation and proximity of the backbones play crucial roles in the interactions and stability of the protein's secondary structure.