Differentiation-dependent interpentameric disulfide bond stabilizes native human papillomavirus type 16

Area of Science:

• Virology
• Molecular Biology
• Biochemistry

Background:

• Human papillomavirus type 16 (HPV16) capsid assembly and integrity depend on conserved L1 cysteine residues.
• Previous studies lacked the temporal context of the natural host environment for HPV.

Purpose of the Study:

• To identify temporal roles for individual L1 cysteine residues in HPV16 capsid maturation within a stratified human tissue model.
• To investigate the impact of cysteine mutations on HPV16 virion stability and infectivity over time.

Main Methods:

• Genetic and biochemical analyses of HPV16 L1 cysteine mutants (C175S, C428S, C185S, C175,185S) in stratified human tissue over 10-20 days.
• Assessment of viral titers, virion stability (nonreducing SDS-PAGE), and endonuclease permeability (Optiprep fractionation).
• Evaluation of infectivity in oxidizing environments.

Main Results:

• C175S mutation significantly reduced HPV16 titers at both 10 and 20 days.
• C428S, C185S, and C175,185S mutations reduced titers only at 20 days.
• Mutant virions showed reduced stability, failed L1 multimerization, and increased endonuclease permeability, indicating a failure to mature.

Conclusions:

• Specific cysteine residues play distinct temporal roles in HPV16 capsid maturation within the natural host environment.
• Cysteine mutations disrupt virion stability and infectivity, leading to a failure in viral maturation.