The fragments of rat amylin rIAPP(17-29) (Ac-VRSSNNLGPVLPP-NH2), rIAPP(17-22) (Ac-VRSSNN-NH2), rIAPP(19-22) (Ac-SSNN-NH2) and rIAPP(17-20) (Ac-VRSS-NH2) together with the related mutant peptides (Ac-VASS-NH2 and Ac-VRAA-NH2) have been synthesized and their copper(II) complexes studied by potentiometric, UV-Vis, CD and EPR spectroscopic methods. Despite the lack of any common strongly coordinating donor functions some of these fragments are able to bind copper(II) ions in the physiological pH range. The longest fragment rat amylin(17-29) keeps one equivalent copper(II) ion in solution in the whole pH range, while two other peptides Ac-VRSSNN-NH2 and Ac-SSNN-NH2 are also able to interact with copper(II) ions in the slightly alkaline pH range. According to the spectral parameters of the complexes, the peptides can be classified into two different categories: (i) the tetrapeptides Ac-VRSS-NH2, Ac-VASS-NH2 and Ac-VRAA-NH2 can interact with copper(II) only under strongly alkaline conditions (pH > 10.0) and the formation of only one species with four amide nitrogen coordination can be detected; (ii) the peptides Ac-VRSSNNLGPVLPP-NH2, Ac-VRSSNN-NH2 and Ac-SSNN-NH2 can form complexes above pH 6.0 with the major stoichiometries [CuH-2L], [CuH-3L]- and [CuH-4L]2-. These data support that rIAPP(17-29) can interact with copper(II) ions under physiological conditions and the SSNN tetrapeptide fragment can be considered as the shortest sequence responsible for metal binding. Density functional theory (DFT) calculations provide some information on the possible coordination modes of Ac-SSNN-NH2 towards the copper(II) ion and suggest that for [CuH-2L], [CuH-3L]- and [CuH-4L]2-, the binding of two, three and four deprotonated amide nitrogens, with NH- of the side chain of asparagine as anchoring group, is probable. Moreover, these data reveal that peptides can be effective metal binding ligands even in the absence of anchoring groups, if more polar side chains are present in a specific sequence.
Copper(II) complexes of rat amylin fragments.
D Sanna;G Pappalardo;E Rizzarelli;
2011
Abstract
The fragments of rat amylin rIAPP(17-29) (Ac-VRSSNNLGPVLPP-NH2), rIAPP(17-22) (Ac-VRSSNN-NH2), rIAPP(19-22) (Ac-SSNN-NH2) and rIAPP(17-20) (Ac-VRSS-NH2) together with the related mutant peptides (Ac-VASS-NH2 and Ac-VRAA-NH2) have been synthesized and their copper(II) complexes studied by potentiometric, UV-Vis, CD and EPR spectroscopic methods. Despite the lack of any common strongly coordinating donor functions some of these fragments are able to bind copper(II) ions in the physiological pH range. The longest fragment rat amylin(17-29) keeps one equivalent copper(II) ion in solution in the whole pH range, while two other peptides Ac-VRSSNN-NH2 and Ac-SSNN-NH2 are also able to interact with copper(II) ions in the slightly alkaline pH range. According to the spectral parameters of the complexes, the peptides can be classified into two different categories: (i) the tetrapeptides Ac-VRSS-NH2, Ac-VASS-NH2 and Ac-VRAA-NH2 can interact with copper(II) only under strongly alkaline conditions (pH > 10.0) and the formation of only one species with four amide nitrogen coordination can be detected; (ii) the peptides Ac-VRSSNNLGPVLPP-NH2, Ac-VRSSNN-NH2 and Ac-SSNN-NH2 can form complexes above pH 6.0 with the major stoichiometries [CuH-2L], [CuH-3L]- and [CuH-4L]2-. These data support that rIAPP(17-29) can interact with copper(II) ions under physiological conditions and the SSNN tetrapeptide fragment can be considered as the shortest sequence responsible for metal binding. Density functional theory (DFT) calculations provide some information on the possible coordination modes of Ac-SSNN-NH2 towards the copper(II) ion and suggest that for [CuH-2L], [CuH-3L]- and [CuH-4L]2-, the binding of two, three and four deprotonated amide nitrogens, with NH- of the side chain of asparagine as anchoring group, is probable. Moreover, these data reveal that peptides can be effective metal binding ligands even in the absence of anchoring groups, if more polar side chains are present in a specific sequence.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
