Nanopore investigation of the stereoselective interactions between Cu(2+) and D,L-histidine amino acids engineered into an amyloidic fragment analogue.

Abstract

Stereochemistry is an essential theme for a number of industries and applications, constructed around discriminating various chiral enantiomers, including amino acids, chiral metal complexes, and drugs. In this work, we designed a set of peptide mutants of the human amyloidic Aβ1-16 sequence, known to display an effective Cu(2+) coordinating pocket provided mainly by the intramolecular His-6, His-13, and His-14 residues, that were engineered to contain L- and D-His enantiomers in positions 6 and 13 and provide a local coordination environment with distinct Cu(2+) binding geometries and affinities. We examined the mechanism of selective chiral recognition of Cu(2+) by such mutant peptides, by quantifying their stochastic sensing in real time with a single α-hemolysin (α-HL) protein immobilized in a planar lipid membrane, while incubated in various concentrations of Cu(2+). Our data reveal that the Cu(2+)-binding affinity lies within the micromolar range, and decreases by orders of magnitude as L-His is replaced with its Denantiomer, with the effect being prevalent when such changes were inflicted on the His-6 residue. The presented results demonstrate the feasibility of tuning the metal selectivity in a relatively simple peptide substrate by enantiomeric replacement of key metal binding residues and illustrates the potential of the protein nanopores as a promising approach to quantify the chiral recognition of l/d amino acids by metals.