A segment spanning residues 684-702 of the PECAM-1 cytoplasmic domain interacts with DPC micelles. (A) The HSQC spectrum of ¹⁵N–labeled PECAM_594-711, generated as described in supplemental Figure 1, reveals its intrinsically unstructured nature. (B) HSQC spectra of ¹⁵N–labeled PECAM_594-711 at DPC concentrations ranging from 0-600mM. Arrows highlight residues that shift and are presumed to participate in DPC binding. (C) PECAM_659-711 HSQC signals in the absence (black) and presence (red) of DPC micelles exhibiting ¹H/¹⁵N chemical shift differences greater than 0.2 ppm are labeled with their single-letter amino acid code and position within full-length human PECAM-1. (D) Plot of the combined ¹H/¹⁵N chemical shift difference for residues of PECAM_659-711 in the absence versus presence of 600mM DPC. Gray bars indicate residues for which backbone resonances were detected in one but not the other sample (and thus, no shift difference could be calculated). Proline 694 is marked with “P,” and residues where it was not possible to make assignments because of missing or overlapping cross peaks are indicated with asterisks. (E) Heteronuclear ¹H-¹⁵N NOE values in the absence (gray) and presence (black) of DPC indicate that residues perturbed by micelles also become more ordered. Residues for which the hetNOE value could not be determined have a value of 0. (F) Three-residue averaged secondary shifts, where (ΔC^α − ΔC^β)_i = 1/3(ΔC_{i − 1}^α + ΔC^α_i + ΔC_{i + 1}^α − ΔC_{i − 1}^β − ΔC^β_i − ΔC_{i + 1}^β), versus residue sequence numbers i.¹⁸  Each ΔC^α and ΔC^β in the equation is the deviation between the experimentally observed and random coil chemical shift value of ¹³C^α and ¹³C^β, respectively.^19,20  Characteristic positive (ΔC^α − ΔC^β) values predict a helix spanning T₆₈₂-Y₇₀₁.