Fig. 4.

Backbone models of two strands of the apolar (residues 1→16) FP region with either (A) in-register parallel 1→16/1→16 or (B) antiparallel 1→15/15→1 β sheet structure. Open blue and red circles are N and CO nuclei, respectively, and closed red circles are the ¹³CO labels used in this study. Some residues are identified. The following distances are used: (1) 3.35 Å between CO nuclei of adjacent residues in a single strand; (2) 5.0 Å between CO nuclei at the same residue position on adjacent strands in the parallel structure; and (3) 4.1 Å between C and N in a CO…HN hydrogen bond. For either model, the length of each dashed line represents 5 Å. For the antiparallel model, the intercarbonyl intermolecular distances for F11–F11 and I4–I4 are 23 Å and 25 Å, respectively, and are indicated by green lines. The L12 – L12 distance is 30 Å.