Interactions between papillomavirus L1 and L2 capsid proteins

Area of Science:

• Virology
• Structural Biology
• Biochemistry

Background:

• The human papillomavirus (HPV) capsid is composed of major capsid protein L1 and minor capsid protein L2.
• Understanding the precise arrangement of L2 within the HPV virion is essential for comprehending viral structure and assembly.

Purpose of the Study:

• To biochemically characterize the domain of L2 responsible for interacting with L1 pentamers.
• To elucidate the nature and stoichiometry of L1-L2 interactions within the HPV capsid.

Main Methods:

• Coexpression of recombinant HPV11 L1 and glutathione S-transferase (GST) L2 fusion proteins in E. coli.
• In vivo binding assays and purification of L1+L2 complexes using GST tags.
• Site-directed mutagenesis to identify critical residues within the L2 L1-binding domain.

Main Results:

• A specific L1-binding domain within HPV11 L2 (amino acids 396-439) was identified.
• The stoichiometry of L1:L2 in purified complexes was determined to be 5:1, indicating one L2 molecule per L1 pentamer.
• Hydrophobic interactions were found to be critical for L1-L2 binding, with disruption observed upon introduction of negative charges.
• L1+L2 complexes facilitated virus-like particle assembly in vitro at pH 5.2 and 6.8, with the latter being non-permissive for L1 alone.

Conclusions:

• L1-L2 interactions are primarily mediated by strong hydrophobic forces within a short L2 domain.
• These interactions significantly influence the in vitro assembly of HPV virus-like particles.
• The findings provide insights into the structural organization of the HPV virion and the role of L2 in assembly.