1. The role of terminal amino group and histidine at the fourth position in the metal ion binding of oligopeptides revisited: Copper(II) and nickel(II) complexes of glycyl-glycyl-glycyl-histamine and its N-Boc protected derivative
Attila Jancsó, Katalin Selmeczi, Patrick Gizzi, Nóra V Nagy, Tamás Gajda, Bernard Henry J Inorg Biochem. 2011 Jan;105(1):92-101. doi: 10.1016/j.jinorgbio.2010.09.004. Epub 2010 Oct 1.
Copper(II) and nickel(II) binding properties of two pseudo tetrapeptides, N-Boc-Gly-Gly-Gly-Histamine (BGGGHa) and Gly-Gly-Gly-Histamine (GGGHa) have been investigated by pH-potentiometric titrations, UV-visible-, EPR-, NMR- and ESI-HRMS (electrospray ionization high resolution MS) spectroscopies, in order to compare the role of N-terminal amino group and imidazole moiety at the fourth position in the complex formation processes. Substantially higher stabilities were determined for the ML complexes of GGGHa, compared to those of BGGGHa, supporting the coordination of the terminal amino group and the histamine imidazole of the non-protected ligand. A dimeric Cu(2)H(-2)L(2) species, formed through the deprotonation of peptide groups of the ligands, was found in the GGGHa-copper(II) system. Deprotonation and coordination of further amide nitrogens led to CuH(-2)L and, above pH~10, CuH(-3)L. Experimental data supports a {NH(2), 2 × N(amide),N(im)} macrochelate structure in CuH(-2)L whereas a {NH(2), 3 × N(amide)} coordination environment in CuH(-3)L. The first two amide deprotonation processes were found to be strongly cooperative with nickel(II) and spectroscopic studies proved the transformation of the octahedral parent complexes to square planar, yellow, diamagnetic species, NiH(-2)L and above pH~9, NiH(-3)L. In the basic pH-range deprotonation and coordination of the amide groups also took place in the BGGGHa containing systems, leading to complexes with a {3 × N(amide),N(im)} donor set, and in parallel the re-dissolving of precipitate. Above pH~11, a further proton release from the pyrrolic NH group of the imidazole ring of BGGGHa occurred providing an additional proof for the different binding modes of the two ligands.
2. Selective control of Cu(II) complex stability in histidine peptides by β-alanine
Justyna Nagaj, Kamila Stokowa-Sołtys, Izabela Zawisza, Małgorzata Jeżowska-Bojczuk, Arkadiusz Bonna, Wojciech Bal J Inorg Biochem. 2013 Feb;119:85-9. doi: 10.1016/j.jinorgbio.2012.11.002. Epub 2012 Nov 15.
The cooperativity of formation of 5-membered and 6-membered chelate rings is the driving force for specificity and selectivity in Cu(II) peptidic complexes. α-Amino acids enable the formation of 5-membered rings, while a 6-membered ring is provided by the coordination of the His side chain imidazole. Introduction of β-alanine is another way of creating a 6-membered ring in the Cu(II) complex. The potentiometric and spectroscopic (UV-vis and CD) study of Cu(II) complexation by a series of four peptides, AAH-am, ABH-am, BAH-am, and BBH-am (where B stands for β-alanine, and -am for C-terminal amide) revealed a very strong effect of the sizes of individual rings, with the order of complex stability AAH-am (5,5,6)>BAH-am (6,5,6)>ABH-am (5,6,6)≫BBH-am (6,6,6). The stabilities of ABH-am and BAH-am complexes are intermediate between those of strong His-3 peptides but these complexes are still able to saturate the coordination sphere of the Cu(II) ion at neutral pH. This fact opens up new possibilities in engineering specific peptide-based chelates.
3. Coordination of Ni2+ and Cu2+ to metal ion binding domains of E. coli SlyD protein
Danuta Witkowska, Daniela Valensin, Magdalena Rowinska-Zyrek, Anna Karafova, Wojciech Kamysz, Henryk Kozlowski J Inorg Biochem. 2012 Feb;107(1):73-81. doi: 10.1016/j.jinorgbio.2011.11.012. Epub 2011 Nov 29.
The C-terminal region of Escherichia coli SlyD is unstructured and extremely rich in potential metal-binding amino acids, especially in histidine residues. SlyD is able to bind two to seven nickel ions per molecule, in a variety of coordination geometries and coordination numbers. This protein contributes to the insertion of nickel into the hydrogenase precursor protein and it has a peptidyl-prolyl cis/trans-isomerase activity which can be regulated through nickel ions. This inspired us to undertake systematic studies on the coordination ability of two histidine-rich peptides from the C-terminus of the SlyD protein with nickel. Also, it is known that histidine-rich regions are part of a Cu(2+) binding domain involved in copper uptake under conditions of metal starvation in vivo in other bacteria. For this reason we decided to examine the complex formation of Ac-AHGHVHGAHDHHHD-NH(2) and Ac-GHGHDHGHEHG-NH(2) fragments with copper ions, which are also reference metal ions in this study. Experiments were performed in a DMSO/water 30:70 solvent. The Ac-AHGHVHGAHDHHHD-NH(2) and Ac-GHGHDHGHEHG-NH(2) fragments were synthesized and their interactions with Ni(2+) and Cu(2+) ions were studied by potentiometric, mass spectrometric, UV-vis, CD, EPR, and NMR spectroscopic techniques in solution. The results show that the Ac-GHGHDHGHEHG-NH(2) fragment forms equimolar complexes with both nickel and copper ions. At physiological pH, the metal ion is bound only through nitrogens from imidazole sidechain of histidine residues. On the contrary, Ac-AHGHVHGAHDHHHD-NH(2) binds 2 metal ions per molecule, at pH range 5 to 7, even if the 1:2 metal:peptide ratios were used. NMR studies indicate the involvement of all His residues in this pH-range in metal binding of the latter peptide. At higher pH, the stoichiometry changes to 1:1 and the His residues are displaced by amide nitrogens.
