In vitro papillomavirus capsid assembly analyzed by light scattering

Area of Science:

• Structural biology
• Virology
• Biochemistry

Background:

• Human papillomavirus (HPV) is a common virus with significant public health implications.
• The L1 major capsid protein is the primary structural component of HPV virions.
• Understanding the self-assembly of L1 proteins into virus-like particles (VLPs) is crucial for vaccine development and antiviral strategies.

Purpose of the Study:

• To investigate the in vitro self-assembly kinetics of human papillomavirus type 11 (HPV11) L1 protein pentamers.
• To determine the nucleation mechanism and subunit addition order during HPV L1 capsid formation.
• To compare the observed assembly pathway with existing models for viral capsid assembly.

Main Methods:

• Purification of HPV11 L1 protein pentamers expressed in E. coli.
• Analysis of in vitro capsid self-assembly kinetics using multi-angle light scattering (MALS).
• Kinetic modeling to determine nucleation size and rate order of subunit addition.

Main Results:

• HPV11 L1 pentamers self-assembled into capsid-like structures in a concentration-dependent manner.
• Capsid formation exhibited sigmoidal kinetics with a lag phase, indicating a nucleation-dependent process.
• Assembly was determined to be second order, with a nucleation size of two pentamers (dimers of pentamers).

Conclusions:

• The data suggest that dimers of L1 pentamers serve as the nucleus for HPV11 capsid assembly.
• Subsequent assembly involves the rapid, sequential addition of single pentamers to the growing capsid structure.
• This finding contrasts with the previously proposed 'five-around-one' nucleation model observed in polyomaviruses.