Fig. 2.

Binding of SspB^154–165 to ZBD₂ as monitored by NMR. (A) A heteronuclear sequential quantum correlation spectrum of 0.25 mM ¹⁵N-labeled ZBD₂ in the absence (black) or presence of 5 mM of SspB^154–165 (red). ∗, chemical shifts that disappear upon addition of peptide. Insets show the NH chemical shift changes of four residues in ZBD₂ in the presence of 0 (black), 0.5 mM (blue), 2.5 mM (green), and 5 mM (red) of SspB^154–165. (B) Shown are the chemical shift changes Δδ^av = [(Δδ_1H)² + (Δδ_15N)²]^1/2 in the presence of 5 mM SspB^154–165. ∗, residues whose chemical shifts disappeared upon addition of 5 mM SspB^154–165. (C) Ribbon and surface representation of ZBD dimer (Protein Data Bank ID code 1OVX) (5). Middle and Bottom are rotated 90^o along the horizontal axis with respect to Top and Middle, respectively. In column 1, helices are colored blue, strands are red, and Zn(II) atoms are shown as pink spheres. In column 2, the electrostatic potential surface of ZBD₂ is shown with negatively charged, positively charged, and hydrophobic surfaces in red, blue, and gray, respectively. In column 3, residues for which Δδ^av > 400 Hz and whose chemical shifts disappeared in the SspB^154–165 titration experiments are colored purple and green, respectively. All structures were drawn by using PyMOL (http://pymol.sourceforge.net).