Figure 4.

Plots of the change of (A) ¹H and (B) ¹⁵N chemical shift for the HN signals occurring upon complexation of CaM with melatonin as a function of residue number. Graph (C) presents a normalized weighed average, [WA], over the chemical shift changes of both ¹H and ¹⁵N, using the formula [WA] = Σ|δ_CaM-Mel – δ_CaM|/2|Δ_max|, where δ_CaM-Mel and δ_CaM are the chemical shifts observed in the complex and in free CaM, and Δ_max is the largest chemical shift change observed for each type of nucleus. The bottom figure (D) shows the mapping of the chemical shift changes onto the structure of CaM (PDB: 4CLN) for N-domain (left panel) and C-domain (right panel). The amino acids that have the larger chemical shift upon melatonin binding are shown with a light gray ball-and-stick model. The Ca²⁺ ions are represented as spheres.