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Molecular modeling of mutations in the DNA-binding domain of the oncoprotein Qin
Sharmila Banerjee-Basu1, Andreas D Baxevanis
1Genome Technology Branch, National Human Genome Research Institute, NIH, Bethesda, Maryland 20892-4470, USA.
Abstract:
The retroviral oncogene qin, homologue of mammalian brain factor 1 (FOXG1 B), belongs to the family of winged helix transcription factors. Oncogenic transformation by Qin requires sequence-specific DNA binding. Missense mutations in the forkhead domain of Qin modulate its oncogenic transforming ability in chicken embryonic fibroblasts. We used homology model building (threading) techniques to generate atomic structures of wild-type c-Qin and c-Qin mutants, using the solution structure of the forkhead domain of the adipocyte transcription factor as a template (M. J. van Dongen et al., J. Mol. Biol., 296: 351-359, 2000). Energy calculations indicate that the Qin forkhead structure is stabilized primarily by hydrophobic interactions between residues at the helical interface. None of the missense mutations analyzed here were responsible for maintaining the most critical pairwise interactions holding the forkhead domain together. The mutated proteins form the overall structure of the forkhead domain, but the mutations do interfere with DNA binding.
Insights
The oncogene Qin, a FOXG1B homolog, requires DNA binding for oncogenic transformation. Mutations in its forkhead domain disrupt DNA binding, affecting its transforming ability in fibroblasts.
Area of Science:
- Molecular Biology
- Oncology
- Structural Biology
Background:
- The retroviral oncogene Qin is a homolog of mammalian brain factor 1 (FOXG1B) and a winged helix transcription factor.
- Oncogenic transformation mediated by Qin is dependent on its ability to bind DNA in a sequence-specific manner.
Purpose of the Study:
- To investigate the structural basis of Qin's oncogenic activity.
- To determine how missense mutations in the forkhead domain of Qin affect its structure and DNA-binding capability.
- To elucidate the role of DNA binding in Qin-induced oncogenic transformation.
Main Methods:
- Homology modeling (threading) techniques were employed to generate atomic structures of wild-type c-Qin and c-Qin mutants.
- The solution structure of the forkhead domain of the adipocyte transcription factor was used as a template for modeling.
- Energy calculations were performed to analyze the stability of the Qin forkhead domain structure.
Main Results:
- The Qin forkhead domain structure is primarily stabilized by hydrophobic interactions at the helical interface.
- None of the analyzed missense mutations disrupted the critical pairwise interactions maintaining the forkhead domain's integrity.
- While mutated proteins retained the overall forkhead domain structure, mutations significantly interfered with DNA binding.
Conclusions:
- Sequence-specific DNA binding is essential for the oncogenic transformation activity of Qin.
- Mutations within the forkhead domain of Qin impair its DNA-binding ability, thereby modulating its oncogenic potential.
- Structural integrity of the forkhead domain is necessary but not sufficient for Qin's oncogenic function; DNA binding is a critical determinant.