The study demonstrates that the tendency of hydrophobic groups to the dense local packing on the surface of β-structural sheets is probably the main reason for the twist of β-structural sheets. To the author's opinion, this fact makes it possible to interpret in a new fashion the architecture of almost all β-structure-containing domains. The majority of β-structure-containing domains are shown to fall into several clearly-outlined groups with the architectural properties depending on the number and mutual disposition along the chain of the elements of secondary structure (β-strands and α-helixes) forming the domain.