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Published on: June 26, 2020
BRCT domain interactions in the heterodimeric DNA repair protein XRCC1-DNA ligase III
1Mutagenesis Laboratory, Imperial Cancer Research Fund, Clare Hall Laboratories, Blanche Lane, South Mimms, Hertfordshire, EN6 3LD, UK.
Abstract:
Proteins involved in DNA repair, or its coordination with DNA replication and mitosis through cell cycle checkpoints, are vital in the concerted cellular response to DNA damage that maintains the integrity of the genome. The "BRCT" domain (BRCA1 carboxy terminal) was noted as a putative protein-protein interaction motif in the breast cancer suppressor gene, BRCA1, and subsequently identified in over 50 proteins involved in DNA repair, recombination, or cell cycle control. The heterodimer of the DNA repair proteins, XRCC1 and DNA ligase III, was the first example of a functional interaction via BRCT modules. The only three-dimensional crystal structure of a BRCT domain was solved for this region of XRCC1. Key amino acid residues mediating the interaction with DNA ligase III were identified here by targeted mutagenesis of the XRCC1 BRCT domain. The consequences of these mutations on protein folding were assessed. A structural model of the DNA ligase III BRCT domain was constructed and similarly tested by mutation of corresponding residues required for the interaction with XRCC1. These data identify the XRCC1-DNA ligase III heterodimer interface and provide the first demonstration of the surface contacts coordinating a functional BRCT-BRCT protein interaction.
Insights
Researchers identified key interactions between DNA repair proteins XRCC1 and DNA ligase III. This study reveals the specific protein contacts coordinating their functional BRCT-BRCT interaction, crucial for genome integrity.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Proteins coordinating DNA repair, replication, and cell cycle checkpoints are vital for genome integrity.
- The BRCA1 C-terminal (BRCT) domain is a protein-protein interaction motif found in over 50 DNA repair and cell cycle control proteins.
- The XRCC1-DNA ligase III heterodimer is the first identified functional interaction mediated by BRCT domains.
Purpose of the Study:
- To identify key amino acid residues and the interface mediating the XRCC1-DNA ligase III heterodimer interaction.
- To understand the structural basis of BRCT-BRCT domain interactions in DNA repair.
Main Methods:
- X-ray crystallography of the XRCC1 BRCT domain.
- Targeted mutagenesis of XRCC1 and DNA ligase III BRCT domains.
- Structural modeling and mutational analysis.
Main Results:
- Identified key amino acid residues in the XRCC1 BRCT domain responsible for DNA ligase III interaction.
- Assessed the impact of mutations on protein folding and interaction.
- Constructed and validated a structural model for the DNA ligase III BRCT domain interaction interface.
- Demonstrated specific surface contacts coordinating the functional BRCT-BRCT interaction.
Conclusions:
- The study elucidates the heterodimer interface between XRCC1 and DNA ligase III.
- Provides the first structural and functional evidence of surface contacts governing BRCT-BRCT protein interactions in DNA repair.
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