Figure 4. The N-terminal extension (residues 1–32) of FKBP38 binds calcium-saturated calmodulin (CaM/Ca²⁺).

(a) An overlay of 2D ¹H-¹⁵N HSQC spectra of CaM/Ca²⁺ (black), and CaM/Ca²⁺ in the presence of the peptide derived from the N-terminus (residues 1–32) of FKBP38 (red). Some of the perturbed residues of calmodulin (BMRB 6542, PDB 1X02) are highlighted with residue numbers. (b) Titration between ¹⁵N labeled FKBP38 N-terminal domain (NTD) with CaM/Ca²⁺. 0.1 mM ¹⁵N labeled NTD was titrated with 0.3 mM calmodulin in the presence of 2.4 mM Ca²⁺. Resonances for NTD are indicated in black and those for NTD + CaM/Ca²⁺ complex are indicated in red. The perturbed residues in the N-terminal extension upon binding CaM/Ca²⁺ are highlighted in a zoomed view of the binding site. The spectra were recorded at 303 K on a 600 MHz equipped with a cryoprobe. (c) The ¹⁵N and ¹H chemical shift changes are combined using the equation Δδ = ((Δδ ¹H)² + (0.154* Δδ ¹⁵N)²)^1/2). A threshold value at 0.02 ppm is indicated by a horizontal dotted line.