Thermochemical and conformational studies of Ni(II) and Zn(II) ternary complexes of alternative metal binding peptides with nitrilotriacetic acid

Energy-resolved threshold collision-induced dissociation (TCID) of negatively-charged [amb5-H+M(II)+NTA-2H]− ternary complexes were studied for how they competitively dissociated into the products [amb5-3H+M(II)]− + NTA or [NTA-3H+M(II)]− amb5, where M = Zn Ni and is nitrilotriacetic acid. The contained one alternative metal binding-5 (amb5) heptapeptides with primary structures acetyl-Aa1-Aa2-Gly3-Pro4-Tyr5-Aa6-Aa7, amino acids Aa1,2,6,7 included potential binding sites Asp, His, and/or Cys. study heptahistidine which represents His affinity tag commonly used in immobilized chromatography (IMAC) separation recombinant proteins. Molecular modeling using PM6 located low energy, geometry-optimized conformers their had collision cross sections that agreed those measured by ion mobility. Using molecular parameters, including vibrational rotational frequencies, reactant from modeling, energy-dependent intensities two product channels modeled a competitive TCID method to determine energies equated 0 K enthalpies (ΔH0). Statistical mechanics thermal corrections provided 298 (ΔH298) Gibbs free (ΔG298) association reactions ↔ amb5 [amb5-H+M(II)+NTA-2H]−. These results compared effective as tags IMAC purification proteins routine can be generally applied compare thermochemistry complexes.