Structure of the yeast Bre1 RING domain

Area of Science:

• Molecular Biology
• Epigenetics
• Structural Biology

Background:

• Histone H2B monoubiquitination at Lys123 (H2Bub1) is a key epigenetic mark regulating vital cellular processes including transcription, DNA repair, and replication.
• The yeast RING E3 ligase Bre1, in complex with the E2 enzyme Rad6, is responsible for catalyzing H2Bub1.
• Understanding the structural basis of Bre1 function is essential for elucidating H2Bub1 regulation and its impact on cellular pathways.

Purpose of the Study:

• To determine the structural features of the yeast Bre1 E3 ligase.
• To investigate the mechanism of Bre1 self-association and its implications for E3 ligase activity.
• To explore potential conserved dimerization mechanisms in human Bre1 homologs.

Main Methods:

• X-ray crystallography was employed to determine the structure of a C-terminal fragment of the yeast Bre1 protein.
• Analysis of the crystal structure revealed specific domains and their interactions.
• Homology modeling was used to predict the structural behavior of human Bre1 orthologs.

Main Results:

• The crystal structure of the Bre1 C-terminal fragment showed a catalytic RING domain preceded by an N-terminal helix.
• This N-terminal helix mediates coiled-coil interactions, facilitating dimerization of Bre1 monomers.
• Homology modeling indicated that human Bre1 homologs, RNF20/RNF40, likely utilize similar coiled-coil interactions for heterodimerization.

Conclusions:

• The N-terminal helix of Bre1 is critical for its dimerization, suggesting a conserved mechanism for E3 ligase assembly.
• Dimerization of Bre1 is likely important for its catalytic activity in H2Bub1.
• The findings provide structural insights into the regulation of histone H2B monoubiquitination and its conservation across species.