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  • Title: Mono-anionic phosphopeptides produced by unexpected histidine alkylation exhibit high Plk1 polo-box domain-binding affinities and enhanced antiproliferative effects in HeLa cells.
    Author: Qian WJ, Park JE, Lim D, Lai CC, Kelley JA, Park SY, Lee KW, Yaffe MB, Lee KS, Burke TR.
    Journal: Biopolymers; 2014 Nov; 102(6):444-55. PubMed ID: 25283071.
    Abstract:
    Binding of polo-like kinase 1 (Plk1) polo-box domains (PBDs) to phosphothreonine (pThr)/phosphoserine (pSer)-containing sequences is critical for the proper function of Plk1. Although high-affinity synthetic pThr-containing peptides provide starting points for developing PBD-directed inhibitors, to date the efficacy of such peptides in whole cell assays has been poor. This potentially reflects limited cell membrane permeability arising, in part, from the di-anionic nature of the phosphoryl group or its mimetics. In our current article we report the unanticipated on-resin N(τ)-alkylation of histidine residues already bearing a N(π)- alkyl group. This resulted in cationic imidazolium-containing pThr peptides, several of which exhibit single-digit nanomolar PBD-binding affinities in extracellular assays and improved antimitotic efficacies in intact cells. We enhanced the cellular efficacies of these peptides further by applying bio-reversible pivaloyloxymethyl (POM) phosphoryl protection. New structural insights presented in our current study, including the potential utility of intramolecular charge masking, may be useful for the further development of PBD-binding peptides and peptide mimetics.
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