Mechanistic Insights into Tunable Metal-Mediated Hydrolysis of Amyloid-beta Peptides

Abstract

An amyloidogenic peptide, amyloid-beta (A beta), has been implicated as a contributor to the neurotoxicity of Alzheimer's disease (AD) that continues to present a major socioeconomic burden for our society. Recently, the use of metal complexes capable of cleaving peptides has arisen as an efficient tactic for amyloid management; unfortunately, little has been reported to pursue this strategy. Herein, we report a novel approach to validate the hydrolytic cleavage of divalent metal complexes toward two major isoforms of A beta (A beta(40) and A beta(42)) and tune their proteolytic activity based on the choice of metal centers (M = Co, Ni, Cu, and Zn) which could be correlated to their anti-amyloidogenic properties. Such metal-dependent tunability was facilitated employing a tetra-N-methylated cyclam (TMC) ligand that imparts unique geometric and stereochemical control, which has not been available in previous systems. Co(II)(TMC) was identified to noticeably cleave A beta peptides and control their aggregation, reporting the first Co(II) complex for such reactivities to the best of our knowledge. Through detailed mechanistic investigations by biochemical, spectroscopic, mass spectrometric, and computational studies, the critical importance of the coordination environment and acidity of the aqua-bound complexes in promoting amide hydrolysis was verified. The biological applicability, of Co(II)(TMC) was also illustrated via its potential blood-brain barrier permeability, relatively low cytotoxicity, regulatory capability against toxicity induced by both A beta(40) and A beta(42) in living cells, proteolytic activity with A beta peptides under biologically relevant conditions, and inertness toward cleavage of structured proteins. Overall,, our approaches and findings on reactivities of divalent metal complexes toward Afi, along with the mechanistic insights, demonstrate the feasibility of utilizing such metal complexes for amyloid control.