Mutational analysis of human papillomavirus type 11 E5a oncoprotein

Area of Science:

• Virology
• Molecular Biology
• Oncology

Background:

• Human papillomavirus type 11 (HPV-11) E5a protein is implicated in cellular transformation.
• The E5 proteins of various papillomaviruses, including HPV-11, are known to interact with the 16,000-molecular-weight (16K) pore-forming protein.

Purpose of the Study:

• To elucidate the structural determinants of HPV-11 E5a transforming activity at the amino acid level.
• To investigate the relationship between E5a's binding affinity to the 16K protein and its transforming potential.

Main Methods:

• Site-directed mutagenesis was employed to create HPV-11 E5a mutants with insertions, deletions, and substitutions.
• Anchorage-independent growth assays were used to assess the transforming activity of wild-type and mutant E5a proteins.
• Co-expression in COS cells and subsequent analysis were performed to evaluate E5a-16K protein binding.

Main Results:

• Substitution of Cysteine-75 in the conserved Cys-X-Cys motif significantly impacted HPV-11 E5a transforming activity, suggesting its importance.
• Mutations altering charge and structure at the COOH terminus markedly impaired transformation, while middle-region changes had milder effects.
• All tested HPV-11 E5a mutants demonstrated binding to the 16K protein, indicating that simple binding is insufficient for transformation.

Conclusions:

• Specific amino acid residues, particularly Cysteine-75, are critical for the transforming activity of HPV-11 E5a.
• The interaction between HPV-11 E5a and the 16K protein is necessary but not sufficient for E5a-mediated cell transformation.
• Structural integrity, especially at the COOH terminus, plays a significant role in the oncogenic function of HPV-11 E5a.