Kowalik-Jankowska Teresa, Rajewska Anna, Jankowska Elzbieta, Grzonka Zbigniew
Faculty of Chemistry, University of Wrocław, Joliot-Curie 14, 50-383, Wrocław, Poland.
Dalton Trans. 2006 Nov 14(42):5068-76. doi: 10.1039/b610619f. Epub 2006 Sep 12.
Stability constants and ligand donor sets of the copper(II) complexes of the NH2-29-56(L1)(AA30GKTKEGVLYV40GSKTKEGVVH50GVATVA56-NH2), NH2-M29-D30-56(L2) and Ac-M29-D30-56(L3) fragments of alpha-synuclein were determined in aqueous solution for 1 : 1 metal-to-ligand molar ratio in the pH range 2.5-10.5. The tyrosine residue in the 39th position of the alpha-synuclein fragments does not take part in the coordination of the metal ion. The potentiometric and spectroscopic data (UV-Vis, CD, EPR) show that acetylation of the amino terminal group induces significant changes in the coordination properties of the L3 fragment compared to that of the L2 peptide. When the amino group is blocked (L3) the imidazole nitrogen of the histidine residue acts as an anchoring site and at higher pH the 3N {N(Im),2N-} and 4N {N(Im),3N-} complexes are formed. The L1 peptide at physiological pH forms in equilibrium 3N {NH2,N-,CO,N(Im)} and 4N {NH2,2N-,N(Im)} complexes. For the L2 peptide the coordination of the copper(II) ions starts from the N-terminal Met residue and with increasing of pH the Asp residue in second position of amino acid sequence coordinates and stabilizes significantly the 2N complex as a result of chelation through the beta-carboxylate group. At physiological pH the 3N {NH2,N-,beta-COO-,N(Im)} coordination mode dominates. At pH above 6 the results for the L2 fragment suggest the formation of 3N and 4N complexes (in equatorial plane) and the involvement of the lateral NH2 group of Lys residue in the axial coordination of Cu(II) ion. In CD spectra sigma (epsilon-NH2-Lys) --> Cu(II) charge transfer transition is observed. The stability constants for the L2 fragment of alpha-synuclein of the 4N {NH2,2N-,N(Im)} and {NH2,3N-} complexes are higher about 1.5 and 0.7 orders of magnitude, respectively, by comparison to those of the L1 peptide. This increase may be explained by the involvement of the epsilon-NH2 group of Lys residue in the coordination sphere of metal ion.
在pH值为2.5 - 10.5的水溶液中，针对1:1的金属与配体摩尔比，测定了α-突触核蛋白的NH2 - 29 - 56（L1）（AA30GKTKEGVLYV40GSKTKEGVVH50GVATVA56 - NH2）、NH2 - M29 - D30 - 56（L2）和Ac - M29 - D30 - 56（L3）片段的铜（II）配合物的稳定常数和配体供体集。α-突触核蛋白片段第39位的酪氨酸残基不参与金属离子的配位。电位滴定和光谱数据（紫外可见光谱、圆二色光谱、电子顺磁共振光谱）表明，与L2肽相比，氨基末端基团的乙酰化会引起L3片段配位性质的显著变化。当氨基被封闭（L3）时，组氨酸残基的咪唑氮作为一个锚定位点，在较高pH值下会形成3N{N(Im),2N - }和4N{N(Im),3N - }配合物。L1肽在生理pH值下形成平衡的3N{NH2,N -,CO,N(Im)}和4N{NH2,2N -,N(Im)}配合物。对于L2肽，铜（II）离子的配位从N端的甲硫氨酸残基开始，随着pH值升高，氨基酸序列第二位的天冬氨酸残基通过β-羧酸盐基团螯合而配位并显著稳定2N配合物。在生理pH值下，3N{NH2,N -,β - COO -,N(Im)}配位模式占主导。在pH值高于6时，L2片段的结果表明形成了3N和4N配合物（在赤道平面），并且赖氨酸残基的侧向NH2基团参与了铜（II）离子的轴向配位。在圆二色光谱中观察到了σ(ε - NH2 - Lys)→Cu(II)电荷转移跃迁。与L1肽相比，α-突触核蛋白L2片段的4N{NH2,2N -,N(Im)}和{NH2,3N - }配合物的稳定常数分别高出约1.5和0.7个数量级。这种增加可能是由于赖氨酸残基的ε - NH2基团参与了金属离子的配位球。
