New insights into the mechanism of nickel superoxide degradation from studies of model peptides

Pascal Heimer,Jana Sartorius,Doreen Mollenhauer,Kevin Herr,Banabithi Koley Seth,Gerd Buntkowsky,Diana Imhof,Daniel Tietze

doi:10.1038/s41598-017-17446-3

Pascal Heimer, Jana Sartorius + Show 6 more

Open Access

https://doi.org/10.1038/s41598-017-17446-3

Copy DOI

Abstract

A series of small, catalytically active metallopeptides, which were derived from the nickel superoxide dismutase (NiSOD) active site were employed to study the mechanism of superoxide degradation especially focusing on the role of the axial imidazole ligand. In the literature, there are contradicting propositions about the catalytic importance of the N-terminal histidine. Therefore, we studied the stability and activity of a set of eight NiSOD model peptides, which represent the major model systems discussed in the literature to date, yet differing in their length and their Ni-coordination. UV-Vis-coupled stopped-flow kinetic measurements and mass spectrometry analysis unveiled their high oxidation sensitivity in the presence of oxygen and superoxide resulting into a much faster Ni(II)-peptide degradation for the amine/amide Ni(II) coordination than for the catalytically inactive bis-amidate Ni(II) coordination. With respect to these results we determined the catalytic activities for all NiSOD mimics studied herein, which turned out to be in almost the same range of about 2 × 106 M−1 s−1. From these experiments, we concluded that the amine/amide Ni(II) coordination is clearly the key factor for catalytic activity. Finally, we were able to clarify the role of the N-terminal histidine and to resolve the contradictory literature propositions, reported in previous studies.

Highlights

Superoxide is constantly formed in aerobic organisms as a byproduct of cellular respiration and represents a highly reactive oxygen species which can cause severe damage to the cell[1]
In contrast to literature reports, we found that catalytic activities for all other nickel superoxide dismutase (NiSOD) mimics studied were in almost the same range of about 2 × 106 M−1 s−1 allowing to conclude that the N-terminal His is not required for catalytic activity, solving a long-standing dispute in the literature
The oxidative environment created by the products of superoxide degradation under which the catalytic activity of these peptides is typically determined, enforced us to question the stability of these model peptides

Summary

Introduction

Superoxide is constantly formed in aerobic organisms as a byproduct of cellular respiration and represents a highly reactive oxygen species which can cause severe damage to the cell[1]. This is rather surprising since the same native-like amine/amide NiSOD mimic was observed to degrade rapidly on air in an early study from the same author[24] From these results and, taking into account the aforementioned theoretical calculations the authors concluded, that the asymmetric amine/amide ligand sphere of the enzyme and the NiSOD metallopeptides must be the key factor in protecting the cysteinate sulfur atoms from oxidation[20]. Except for these two studies no systematic analysis of the stability of the NiSOD mimic was performed far[13,20]. We were able to unveil the role of the N-terminal histidine (Fig. 1, peptides 2, 3, 5 and 6) clarifying contradictory literature reports[15,16,17]

Methods

Results

Discussion

Conclusion