Design and synthesis of inhibitors targeting methyllysine reader proteins belonging to the polycomb paralog family
Date
2019-06-06
Authors
Milosevich, Natalia
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Abstract
Methyl reader proteins recognize and bind to post-translationally methylated
residues and have functional roles in diverse cellular processes including gene regulation,
development and oncogenesis. The CBX polycomb paralog family of methyllysine
readers recognize trimethyllysine lysine residues on histone tail 3 and repress
transcription by compacting chromatin. The polycomb paralogs form multi-protein
complexes that silence the expression of tumour suppressor genes, and play important
roles in regulating cell cycle and differentiation. Each paralog is structurally similar, yet
has distinct functions, of which many are unknown.
My work has focused on the design and synthesis of CBX inhibitors and on the
development of new methodologies for the discovery of inhibitors targeting methyllysine
readers. In this work, I report on a series of potent peptidic inhibitors that selectively
target the CBX polycombs, as well as the first selective inhibitor for the family member
CBX6, and dual-active inhibitors that target CBX6/CBX8. The results demonstrate the
potential to achieve selectivity through interactions outside of the methyllysine binding
domain. Structural determinants in the binding pocket of each protein that differ within
the family and give rise to selectivity were discovered. I will also report on a series of
peptidomimetic CBX inhibitors that are active in cells. Cellular active inhibitors are
critical for understanding the biological role of each CBX protein and their potential as
therapeutic targets.
New high-throughput approaches are needed to efficiently target methyllysine
readers by chemical inhibition. I describe in this work a strategy for creating massive
libraries of phage-displayed peptidic inhibitors containing methyllysine mimics.
Synthetic optimization on cysteine-containing peptide phage constructs allowed for the
successful installation of Kme3 mimics. This is the first report of a post-translational
methylated peptide phage library. The methodology I developed can be used in a
synthetic chemistry-driven adaptation of traditional phage display for the screening of
millions of peptide-based compounds. Strategies that allow for diversity and high
throughput screening will aid in future efforts in targeting the highly similar CBX
proteins.
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Keywords
epigenetics, peptidomimetics, polycomb paralog proteins, methyllysine reader proteins