Fig. 3.

Residue-specific 3D structures for Mini-B (MB) in either HFIP solutions (a, b) or SDS micelles (c) determined using ¹³C-FTIR or 2D-NMR spectroscopy. PyMOL representations of peptide backbones are shown as either thick (N- and C-terminal α-helices) ribbons or thin green (turn regions) ribbons; amino acid side-chains are represented as wireframes. Polar residues are colored blue, with nonpolar and cysteine residues in red and yellow, respectively. a The ¹³C-FTIR structure for oxidized MB, disulfide-linked at Cys-8 to Cys-40 and Cys-11 to Cys-34 (see bottom left; S-MB numbering) (PDB Accession Code: 1SSZ). The β-turn connecting the N-terminal (foreground) and C-terminal (background) α-helices is shown in green. b The 2D-NMR structure for reduced MB with no disulfide-links and the Cys-8 on the left and the Ser-41 on the right (PDB: 2JOU). c The 2D-NMR structure for oxidized MB with disulfide links associated with an SDS micelle; SDS molecules are modeled as stick figures, with their fatty acyl groups in green and polar headgroups in red (PDB: 2DWF). The N- and C-terminal helices of oxidized MB in either a or c reproduce the folding of these domains in homology-modeled SP-B (see Fig. 1).