Coordination of Two High-Affinity Hexamer Peptides to Copper(II) and Palladium(II) Models of the Peptide−Metal Chelation Site on IMAC Resins

Abstract

The coordination of peptides Ser-Pro-His-His-Gly-Gly (SPHHGG) and (His)6 (HHHHHH) to [PdII(mida)(D2O)] (mida2- = N-methyliminodiacetate) was studied by 1H NMR as model reactions for CuII(iminodiacetate)-immobilized metal affinity chromatography (IMAC) sites. This is the first direct physical description of peptide coordination for IMAC. A three-site coordination is observed which involves the first, third, and fourth residues along the peptide chain. The presence of proline in position 2 of SPHHGG achieves the best molecular mechanics and bonding angles in the coordinated peptide and enhances the interaction of the serine amino nitrogen. Histidine coordination of H1, H3, and H4 of (His)6 and H3 and H4 of SPHHGG was detected by 1H NMR contact shifts and H/D exchange of histidyl protons. The EPR spectra of SPHHGG and HHHHHH attached to the [CuII(mida)] unit were obtained for additional modeling of IMAC sites. EPR parameters of the parent [Cu(mida)(H2O)2] complex are representative: gzz = 2.31; gyy = 2.086; gxx = 2.053; A parallel = 161G; AN = 19G (three line, one N coupling). Increased rhombic distortion is detected relative to the starting aqua complex in the order of [Cu(mida)L] for distortion of HHHHHH > SPHHGG > (H2O)2. The lowering of symmetry is also seen in the decrease in the N-shf coupling, presumably to the imino nitrogen of mida2- in the order 19 G (H2O), 16 G (SPHHGG) and 11 G (HHHHHH). Visible spectra of the [Cu(mida)(SPHHGG)] and [Cu(mida)(HHHHHH)] as a function of pH indicate coordination of one histidyl donor at ca. 4.5, two in the range of pH 5-7, and two chelate ring attachments involving the terminal amino donor for SPHHGG or another histidyl donor of HHHHHH in the pH domain of 7-8 in agreement with the [PdII(mida)L] derivatives which form the two-chelate-ring attachment even at lower pH as shown by the 1H NMR methods.

Copper(II), nickel(II) and zinc(II) complexes of N-acetyl-His-Pro-His-His-NH2: Equilibria, solution structure and enzyme mimicking

“…The large separation of pK 101 and pK [1][2][3][4][5][6][7][8][9][10][11] , and the small change in the Vis, CD and EPR spectra of the CuH À2 L species compared to [CuH À1 L] + indicates the formation of a mixed hydroxo ligand complex with {N im , N À amide , N im , OH À ) type coordination (Scheme 1). The pK 1-11 for the [CuH À1 L] + = CuH À1 L(OH) + H + process is 8.26, that is one unit lower, than e.g.…”

“…doi:10.1016/j.jinorgbio.2008.01.006 their surface [5][6][7]. Moreover, H and H/P-rich sequences like hexahistidine or GHPHHG have been playing important role in anchoring and purifying proteins on metal ionaffinity chromatography [8][9][10].…”

Comparison of Energy-Minimized Structures of [PdII(N-methyliminodiacetate)] Complexes of X1-His-X3-His-His Peptides as an Analysis of Steric and Specific Interactions with Synthetic Binding Tags for IMAC Separations

“…A commonly used IMAC column has Cu II , Ni II , or Zn II sites supported by iminodiacetate chelation that is attached to a resin support (1)(2)(3). [Pd II (mida)(peptide)] complexes, mida 2-) N-methyliminodiacetate, have been useful for NMR purposes in modeling the coordination of peptides to IMAC binding sites (9,10). It was shown that the carboxylate donors from the mida 2-portion of the molecule are displaced as the peptide chain establishes a three-point contact via the remaining square-planar coordination positions of the Pd II center as shown in the figure for the Ser-Pro-His-His-Gly-Gly peptide (SPH-HGG) (9).…”

“…[Pd II (mida)(peptide)] complexes, mida 2-) N-methyliminodiacetate, have been useful for NMR purposes in modeling the coordination of peptides to IMAC binding sites (9,10). It was shown that the carboxylate donors from the mida 2-portion of the molecule are displaced as the peptide chain establishes a three-point contact via the remaining square-planar coordination positions of the Pd II center as shown in the figure for the Ser-Pro-His-His-Gly-Gly peptide (SPH-HGG) (9). EPR spectra of the Cu II analogue, [Cu II (mida)-(peptide)], confirm a similar structure for the Cu II -ida IMAC site models (9,10).…”

“…It was shown that the carboxylate donors from the mida 2-portion of the molecule are displaced as the peptide chain establishes a three-point contact via the remaining square-planar coordination positions of the Pd II center as shown in the figure for the Ser-Pro-His-His-Gly-Gly peptide (SPH-HGG) (9). EPR spectra of the Cu II analogue, [Cu II (mida)-(peptide)], confirm a similar structure for the Cu II -ida IMAC site models (9,10). A molecular mechanics calculation for the structure of the shorter SPHHG peptide complex, [Pd II (mida)(SPHHG)], which is related to the pentapetides of the present study, was carried out by the Spartan program using the MMFF94 force field.…”