Figure 2.

(a) Region of a ¹⁵NH HSQC-TROSY spectrum of the c-E-helix-PYP monomer (red) and the monomer containing 5-F-Trp (blue). Residue numbers are indicated. (b) Model of the c-E-helix-PYP monomer with residues whose NH chemical shifts are affected by fluorine substitution (except those on the same strand as 5-F-Trp) colored blue. Residues shown in the HSQC detail (a) are labeled and shown as sticks. The fluorine atom is shown as a green sphere on a stick representation of the 5-F-Trp side chain. The E-helix sequence is colored magenta. (c) Same region as in panel a of a ¹⁵NH HSQC-TROSY spectrum showing the c-E-helix-PYP dimer labeled with ¹⁵N only (green) and the heterodimer sample (blue). The heterodimer sample is a mixture of three molecular species: (1) dimers made from two ¹⁵N-labeled monomers, (2) dimers made from two ¹⁹F-labeled monomers, and (3) dimers made from one ¹⁵N-labeled monomer and one ¹⁹F-labeled monomer. Species (2) is invisible in the NH HSQC spectrum, but both species 1 and 3 are present. The same subset of resonances is affected by fluorine substitution as for the monomer. (d) Model of the c-E-helix-PYP domain-swapped dimer with one monomer colored white and the other green. The E-helix sequence is colored magenta. Residues affected by fluorine substitution are colored blue.