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Updated: Jun 8, 2026

Characterization of Multi-subunit Protein Complexes of Human MxA Using Non-denaturing Polyacrylamide Gel-electrophoresis

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Dimerization of a viral SET protein endows its function.

Hua Wei¹, Ming-Ming Zhou

¹Department of Structural and Chemical Biology, Mount Sinai School of Medicine, 1425 Madison Avenue, Box 1677, New York, NY 10029, USA.

Proceedings of the National Academy of Sciences of the United States of America

|October 13, 2010

Summary

This summary is machine-generated.

Paramecium bursaria chlorella virus SET (vSET) methyltransferase suppresses host transcription by methylating histone H3 at lysine 27 (H3K27). This study reveals vSET

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Area of Science:

Epigenetics and molecular biology
Structural biology and enzymology

Background:

Histone modifications, particularly lysine methylation, are crucial epigenetic regulators of gene transcription.
Paramecium bursaria chlorella virus encodes vSET, a SET domain methyltransferase that silences host genes via H3K27 methylation.
The dimeric nature and mechanism of vSET activity, unlike mammalian KMTs, remain poorly understood.

Purpose of the Study:

To elucidate the molecular mechanism underlying the dimeric function of vSET.
To understand how vSET achieves negative cooperativity and substrate specificity in H3K27 methylation.
To reveal the structural basis for vSET's unique mode of action.

Main Methods:

Determined atomic structures of vSET in its free form and as a ternary complex with S-adenosyl homocysteine and an H3 peptide.
Performed biochemical analyses to investigate enzyme kinetics and cooperativity.
Utilized structural and biochemical data to propose a mechanistic model for vSET activity.

Main Results:

Demonstrated that dimeric vSET exhibits negative cooperativity between its two active sites, methylating H3K27 one site at a time.
Identified the structural basis for negative cooperativity and H3K27 substrate specificity.
Proposed a 'walking' mechanism where vSET independently methylates host H3K27 globally.

Conclusions:

vSET employs a unique dimeric mechanism with negative cooperativity for H3K27 methylation.
This mechanism allows vSET to function autonomously in global host gene silencing.
Contrasts with mammalian EZH2, which requires a complex for similar epigenetic regulation.