Histidine methyltransferase SETD3 methylates structurally diverse histidine mimics in actin

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Actin histidine N^τ-methylation by histidine methyltransferase SETD3 is crucial in human biology and disease.
• Understanding SETD3's substrate specificity and catalytic mechanisms is essential.

Purpose of the Study:

• To investigate the substrate scope of human SETD3 beyond histidine.
• To elucidate the binding and catalytic mechanisms of SETD3 with histidine mimics.

Main Methods:

• Integrated synthetic, biocatalytic, and biostructural analyses.
• Enzyme assays and X-ray crystallography.
• Quantum mechanical/molecular mechanical molecular dynamics and free-energy simulations.

Main Results:

• SETD3 exhibits a broader substrate scope, methylating N-nucleophiles on aromatic and aliphatic side chains, not just histidine.
• Biostructural and computational analyses revealed binding geometries and free energy barriers for methyl transfer to histidine mimics.
• Histidine remains the superior substrate compared to its analogs for SETD3.

Conclusions:

• Human SETD3 can efficiently methylate several histidine mimics, expanding its known biological function.
• This study provides significant mechanistic, biocatalytic, and functional insights into actin histidine methylation by SETD3.