Section 22.2.5.3.2. β-sheets

β-sheets consist of short strands of polypeptide (typically 5–7 residues) running parallel or antiparallel and cross-linked by N—H···O=C hydrogen bonds. Although the (φ, ψ) angles of residues within β-sheets can be quite variable, the hydrogen-bonding patterns within these segments tend to be quite regular, as in the original Pauling models (Pauling & Corey, 1951). Occasional β-bulges in the middle of β-strands can interrupt the hydrogen-bonding pattern (Richardson et al., 1978), but otherwise disruptions occur only at the ends of strands. The hydrogen bonds in β-sheets appear to be slightly shorter than those in helices, by ∼0.1 Å, and also more linear (N—H···O ∼ 160°, compared with ∼157° in helices) (Baker & Hubbard, 1984). There also appears to be no difference between parallel and antiparallel β-sheets in the hydrogen-bond lengths and angles.