Structure and stability of beta-pleated sheets.

Beside alpha-helices, beta-sheets are the most common secondary structure elements of proteins. In this article, the question of structure and stability of parallel and antiparallel sheets of various lengths is addressed. All data obtained are compared to a selected set of protein structures. In antiparallel beta-sheets, one of the two possible H-bonded structures (containing 14 atoms in the H-bonded pseudoring) is energetically more favored and also more abundant in proteins than the other one (with 10 atoms involved in the pseudoring). Parallel beta-sheets and their subunits are energetically less stable and indeed found to occur more rarely in proteins. Antiparallel hairpins are disfavored compared to beta-sheets formed by sequentially separated strands. Agreement between theory and experimental data indicates that characterization of structural building blocks at an appropriately accurate level of theory is a useful tool to get insight into fundamentals of protein structure.