Multiple TPR motifs characterize the Fanconi anemia FANCG protein

Area of Science:

• Genetics and Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Fanconi anemia (FA) is a genetic disorder characterized by genomic instability.
• The FA pathway, essential for DNA repair, involves monoubiquitylation of FANCD2.
• A nuclear core complex of FANC proteins, including FANCG, is critical for this pathway, but FANCG's structure was poorly understood.

Purpose of the Study:

• To investigate the structural and functional domains of the FANCG protein within the FA core complex.
• To identify potential protein-protein interaction motifs in FANCG.
• To elucidate the role of FANCG structure in the FA pathway.

Main Methods:

• Homology searches comparing human FANCG with orthologs in zebrafish and rice fish.
• Identification and analysis of tetratricopeptide repeat (TPR) motifs in FANCG.
• Site-directed mutagenesis of identified TPR motifs.
• Functional complementation assays in FA-G lymphoblasts.
• Co-immunoprecipitation assays to assess protein interactions (FANCG-FANCA).

Main Results:

• At least seven tetratricopeptide repeat (TPR) motifs were identified in the FANCG protein.
• Missense mutations disrupting TPR1, TPR2, TPR5, and TPR6 led to loss of FANCG function and impaired complementation of the FA phenotype.
• Mutant FANCG proteins showed reduced or abolished binding to FANCA.
• The TPR4 mutant exhibited reduced FANCA interaction, suggesting its functional relevance.

Conclusions:

• FANCG is a typical TPR protein, functioning as a scaffold in protein-protein interactions.
• TPRs in FANCG are critical for its function in the FA pathway, particularly for its interaction with FANCA.
• These findings highlight the structural basis for FANCG's role in the assembly and stability of the FA core complex, advancing our understanding of genome protection mechanisms.