Role of L2 cysteines in papillomavirus infection and neutralization

Ratish Gambhira,Subhashini Jagu,Richard Roden,Patricia M Day,Balasubramanyam Karanam

doi:10.1186/1743-422x-6-176

Abstract

Vaccination of mice with minor capsid protein L2 or passive transfer with the L2-specific neutralizing monoclonal antibody RG-1 protects against human papillomavirus type 16 (HPV16) challenge. Here we explored the nature of the RG-1 epitope and its contribution to viral infectivity. RG-1 bound equivalently HPV16 L2 residues 17-36 with or without an intact C22-C28 disulphide bridge. HPV16 L2 mutations K20A, C22A, C22S, C28A, C28S, or P29A prevented RG-1 binding, whereas Y19A, K23A or Q24A had no impact. Mutation of either C22 or C28 to alanine or serine compromises HPV16 pseudoviral infectivity both in vitro and in the murine vaginal tract, but does not impact pseudovirion assembly. Despite their lack of infectivity, HPV16 pseudovirions containing C22S or C28S mutant L2 bind to cell surfaces, are taken up, and expose the 17-36 region on the virion surface as for wild type HPV16 pseudovirions suggesting normal furin cleavage of L2. Mutation of the second cysteine residue in Bovine papillomavirus type 1 (BPV1) L2 to serine (C25S) dramatically reduced the infectivity of BPV1 pseudovirions. Surprisingly, in contrast to the double mutation in HPV16 L2, the BPV1 L2 C19S, C25S double mutation reduced BPV1 pseudovirion infectivity of 293TT cells by only half.

Highlights

The binding of virions to cell surfaces, presumably via heparan sulfate proteoglycans [5], promotes furin cleavage of L2, and this can occur on the cell surface
Virology Journal 2009, 6:176 http://www.virologyj.com/content/6/1/176 types [8], but here we focus upon human papillomavirus type 16 (HPV16) because it is associated with a half of cervical cancer cases and the majority of human papillomavirus (HPV)+vaginal, vulval, penile, anal, and head and neck cancers [9]
(Table 1) rather than inefficient furin cleavage of the C22S or C28S mutant L2 in HPV16 pseudovirions. These findings suggest that the C22 and C28 residues are not required for exposure of this epitope during HPV16 infection

Summary

Introduction

Western blot analysis of purified HPV16 pseudovirions revealed similar levels of wild type and deletion mutant HPV16 L2 were present, suggesting that none of the small deletions within L2 adversely impacted L1/L2 co-assembly into particles. Western blot analysis of purified HPV16 pseudovirions revealed similar levels of wild type and point mutant HPV16 L2 were present (Table 1), suggesting that none of the point mutations within L2 adversely impacted L1/L2 co-assembly into HPV16 pseudovirion particles.

Results

Conclusion