The role of copper(II) and zinc(II) in the degradation of human and murine IAPP by insulin-degrading enzyme

Abstract

Amylin or islet amyloid polypeptide (IAPP) is a 37-residue peptide hormone secreted from the pancreatic islets into the blood circulation and is cleared by peptidases in the kidney. IAPP aggregates are strongly associated with β-cell degeneration in type 2 diabetes, as demonstrated by the fact that more than 95% of patients exhibit IAPP amyloid upon autopsy. Recently, it has been reported that metal ions such as copper(II) and zinc(II) are implicated in the aggregation of IAPP as well as able to modulate the proteolytic activity of IAPP degrading enzymes. For this reason, in this work, the role of the latter metal ions in the degradation of IAPP by insulin-degrading enzyme (IDE) has been investigated by a chromatographic and mass spectrometric combined method. The latter experimental approach allowed not only to assess the overall metal ion inhibition of the human and murine IAPP degradation by IDE but also to have information on copper- and zinc-induced changes in IAPP aggregation. In addition, IDE cleavage site preferences in the presence of metal ions are rationalized as metal ion-induced changes in substrate accessibility.

A neglected modulator of insulin-degrading enzyme activity and conformation: The pH

“…MS results confirm that such different binding features affect IDE capability to degrade insulin, as the enzyme is inactive toward the hormone at acidic pH. Moreover, the insulin fragments detected by MS at basic pH involve the C-terminal residues of the insulin A chain [A (14-21) and A (15)(16)(17)(18)(19)(20)(21)] and the fragments B (17-24) and B (17)(18)(19)(20)(21)(22)(23)(24)(25). The same set of insulin fragments are known to be produced in solutions containing IDE at high concentrations, where the equilibrium in the oligomerization state of the enzyme is mainly shifted toward the dimeric and/or tetrameric forms.…”

“…Interestingly, apart from the changes on the overall activity, it is possible to note that the insulin fragments detected at alkaline pH are different from the ones detected at physiological pH. Particularly, the insulin fragments involving the C-terminal residues of the insulin B (17)(18)(19)(20)(21)(22)(23)(24)(25) are mainly produced at alkaline pH [15]. The same set of insulin fragments are known to be produced in solutions containing IDE at high concentrations [15] and therefore it is easy to speculate that the pH, as well as the enzyme concentration, has an effect on IDE oligomerization state, acidic pH shifting the equilibrium toward the monomeric form.…”

“…Indeed, considerable evidence suggests that IDE inhibitors may hold therapeutic value, particularly for type 2 diabetes and other disorders involving impaired insulin signaling [12], while IDE activators could be used as possible drugs aiming at lowering Aβ levels in AD [13]. Moreover, the effect that other experimental factors such as oligomerization state [14][15][16], presence of metal ions [17][18][19][20] and oxidative stress [21][22][23] can have on IDE activity has also been widely investigated.…”

Potentiometric and spectroscopic studies on the copper(ii) complexes of rat amylin fragments. The anchoring ability of specific non-coordinating side chains

“…The inhibition of the aggregation was shown in several studies [1][2][3] , while the impact of copper mediated ROS production was demonstrated in other works [4][5][6] . Moreover, it was also reported that copper(II) is able to modulate the proteolytic activity of IAPP degrading enzymes 7 . The biological significance of hIAPP promoted the investigations on the coordination chemistry of these peptides [8][9] but the low solubility of the peptide fragments hindered these studies.…”

Mass spectrometry is a multifaceted weapon to be used in the battle against Alzheimer's disease: Amyloid beta peptides and beyond

“…In some cases, the latter can have a very different function from the precursor peptide, and their specific formation depends also on the environmental conditions experienced by the particular proteases that act on the peptides. Indeed, types and abundances of the cryptic peptides generated from a precursor protein (Aβ protein in our case) can be widely affected by the presence of metal ions, small molecules, and pH . For this reason, detailed studies of the relative abundances of the Aβ peptides are of paramount importance, because they could potentially and indirectly unveil other biomolecular mechanisms altered in AD, which are not feasible to investigate.…”