Elastic effects behind cooperative bonding in beta-sheets.

We present extensive density functional theory calculations of the bonding between strands in beta-sheets. We identify a significant cooperative effect whereby the interaction increases in strength with the number of strands. We show that the effect is related to a coupling between interstrand bonding and intrastrand elastic properties. It is found that a direct consequence of this coupling is that the pitch of beta-sheets should contract with increasing number of strands, and we show that the effect can be observed directly in experimental data from the Protein Data Bank.