Trimethyllysine is an important post-translationally modified amino acid with functions in the carnitine biosynthesis and regulation of key epigenetic processes. Protein lysine methyltransferases and demethylases dynamically control protein lysine methylation, with each state of methylation changing the biophysical properties of lysine and the subsequent effect on protein function, in particular histone proteins and their central role in epigenetics. Epigenetic reader domain proteins can distinguish between different lysine methylation states and initiate downstream cellular processes upon recognition. Dysregulation of protein methylation is linked to various diseases, including cancer, inflammation, and genetic disorders. In this review, we cover biomolecular studies on the role of trimethyllysine in carnitine biosynthesis, different enzymatic reactions involved in the synthesis and removal of trimethyllysine, trimethyllysine recognition by reader proteins, and the role of trimethyllysine on the nucleosome assembly.

SARS-CoV-2 Spike protein RBD interacts with the hACE2 receptor to initiate cell entry and infection. We set out to develop lactam-based i,i + 4 stapled hACE2 peptides targeting SARS-CoV-2. In vitro screening demonstrates the inhibition of the Spike protein RBD-hACE2 complex formation by the hACE2_21-55A36K-F40E stapled peptide (IC₅₀: 3.6 μM, K_d: 2.1 μM), suggesting that hACE2 peptidomimetics could form the basis for the development of anti-COVID-19 therapeutics.

Application of structurally and chemically diverse unnatural amino acids in biomolecular studies of lysine posttranslational modifications is described in this Feature Article.

SETD3-catalysed N³-methylation of His73 in β-actin plays a key role in stabilisation of actin filaments in the metazoan cells. Overexpression and/or dysregulation of SETD3 is associated with several human pathologies, including cancer. Here, we examined the role of the Ile71 residue in β-actin on human SETD3 catalysis. Substitution of Ile71 in β-actin peptides by its natural and unnatural mimics reveals that the ‘secondary’ Ile71 binding pocket modulates the substrate efficiency of β-actin. Our enzymatic work demonstrates that human SETD3 can accommodate structurally diverse hydrophobic side chains in its Ile71 binding pocket, providing clear limits of the size and shape of Ile analogues. Water thermodynamics calculations reveal that the Ile71 pocket is occupied by high-energy water molecules, that are released upon the Ile71 binding, contributing favourably to the SETD3-βA complex formation. The work highlights that the hydrophobic Ile71 binding site plays an essential role in SETD3 catalysis, contributing to an ongoing effort in the design and development of chemical probes targeting SETD3.

Histone peptides containing easily accessible amide-derived lysine mimics display substrate and inhibition selectivity for biomedicinally important histone lysine methyltransferases over acetyltransferases.