Correction

BIOPHYSICS. For the article “Tryptophan zippers: Stable, monomeric β-hairpins,” by Andrea G. Cochran, Nicholas J. Skelton, and Melissa A. Starovasnik, which appeared in number 10, May 8, 2001, of Proc. Natl. Acad. Sci. USA (98, 5578–5583; First Published May 1, 2001; 10.1073/pnas.091100898), the authors note the following. Quantitative analysis of the ¹H chemical shifts using the Sander module of AMBER 6.0 reveals that the frequencies of the Hβ and Hɛ3 resonances of Trp4 and Trp11 (for trpzips 1 and 2) and Trp5 and Trp14 (for trpzip4) are inconsistent with the side chain orientations previously determined. Instead, refinement of the structures based not only on NOE-derived distance restraints and dihedral angle restraints, but also on ¹H chemical shift-based restraints, indicates that the side chains for these residues actually reside primarily in the 180° χ1 rotamer well, not the −60° rotamer previously indicated. Refined coordinates are available in the Protein Data Bank, www.rcsb.org [PDB ID codes 1LE0 (trpzip1), 1LE1 (trpzip2), and 1LE3 (trpzip4)]. The updated coordinates are very similar to those determined previously; as before, for all three peptides, the two strands are highly twisted. The important difference, however, is that each pair of cross-strand tryptophan rings now shows edge-to-face packing against one another (see Fig. 1) that is conserved among all three trpzip peptides regardless of turn-type.

Figure 1.

Representative structure of trpzip1 refined using ¹H chemical shift-based restraints. Edge-to-face packing is observed for Trp11/Trp2 and Trp4/Trp9 cross-strand pairs.