The Extreme C-terminus of Xeroderma pigmentosum group G protein Mediates Protein-Protein Interactions

Author:  Kiran Rangaraj
Institution:  University of California, Berkeley

Organisms across the evolutionary scale are equipped with complex and interconnected DNA repair pathways that are regulated by multifunctional proteins. These proteins mediate interactions by conformational changes and protein hand-offs in order to coordinate lesion detection and removal with vital cellular processes such as DNA replication, transcription and recombination. Mutations that disrupt repair protein functioning can lead to genomic instability, developmental and immunological abnormalities, and cancer and aging. Xeroderma pigmentosum group G (XPG) is one such multifunctional protein that plays a critical role in maintaining human genome stability. Point mutations in the XPG gene gives rise to an inherited photosensitive disorder, Xeroderma pigmentosum (XP) and truncation mutations cause the profound neurological and developmental disorder Cockayne syndrome (CS) combined with XP. The molecular basis of XPG in XP is well understood because XPG contains structure specific 3ˈ endonuclease activity that is critical to the repair of ultraviolet-damaged DNA in the nucleotide excision repair (NER) pathway. However, the clinical features of CS in XPG-CS patients are difficult to explain on the basis of defects in NER, which suggests that XPG possesses several poorly understood roles that are regulated by its unstructured non-enzymatic recognition (R) and carboxyl (C) terminal domains. These domains have been shown to mediate interactions with over fifteen proteins from multiple repair pathways. Studies conducted on these regions have identified novel scaffolding roles for XPG in transcription-coupled (TCR) and base excision (BER) repair, and recently a replication-associated function with proteins that process damaged replication forks. How XPG is involved in multiple pathways is of considerable interest. Considering the role of the XPG C-terminus in protein-protein interaction, this study involved bacterially expressing and purifying three sequential C-terminal subdomain constructs and screening interactions with seven proteins representing roles in different DNA replication and repair pathways. All seven proteins were found to interact with the same region of the C-terminus, which provides information critical towards identifying the amino acids uniquely required by each protein partner. This will allow one to genetically dissect the molecular basis of XPG in order to elucidate and remedy its involvement in the complex disease phenotype of XP-CS.

The Journal of Young Investigators is not affiliated with the US Department of Energy. This paper was written by a student intern with the Department of Energy and does not constitute a declarative position of either the Department of Energy or the Journal of Young Investigators.