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Folding of unstructured peptoids and formation of hetero-bimetallic peptoid complexes upon side-chain-to-metal coordination

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Abstract

Helices are key structural features in biopolymers, enabling a variety of biological functions. Mimicking these secondary structure motifs has wide potential in the development of biomimetic materials. Peptoids, N-substituted glycine oligomers, are an important class of peptide mimics that can adopt polyproline type helices if the majority of their sequence consists of chiral bulky pendent groups. Such side-chains are structure inducers but they have no functional value. We present here the inclusion of several metal-binding groups in one peptoid oligomer as a new platform towards the development of functional helical peptoids. Thus, we describe the coordination of two metal ions to unstructured peptoids incorporating four 8-hydroxyquinoline (HQ) ligands at fixed positions as two (HQ, HQ) metal binding sites, and a mixture of chiral benzyl and alkyl substituents in varied positions along the peptoid backbone. For the first time, we demonstrate by circular dichroism spectroscopy, solution NMR techniques and high-level DFT calculations that some of these unstructured peptoids can fold upon metal binding to form helical structures. Replacing one HQ ligand with a terpyridine (Terpy) ligand resulted in unique sequences that can selectively coordinate Cu2+ to the (Terpy, HQ) and Zn2+ (or Co2+) to the (HQ, HQ) sites from a solution mixture containing Cu2+ and Zn2+ (or Co2+) ions. Interestingly, the binding of Cu2+ to the (Terpy, HQ) site in one of these peptoids can initiate a conformational change that in turn facilitates the coordination of Zn2+ (or Co2+) ions to the (HQ, HQ) site, demonstrating a unique example of positive allosteric cooperativity in peptide mimics.

Graphical abstract: Folding of unstructured peptoids and formation of hetero-bimetallic peptoid complexes upon side-chain-to-metal coordination

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Publication details

The article was received on 14 Aug 2018, accepted on 16 Oct 2018 and first published on 17 Oct 2018


Article type: Edge Article
DOI: 10.1039/C8SC03616K
Citation: Chem. Sci., 2019, Advance Article
  • Open access: Creative Commons BY-NC license
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    Folding of unstructured peptoids and formation of hetero-bimetallic peptoid complexes upon side-chain-to-metal coordination

    M. Baskin, H. Zhu, Z. Qu, J. H. Chill, S. Grimme and G. Maayan, Chem. Sci., 2019, Advance Article , DOI: 10.1039/C8SC03616K

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