We have previously demonstrated that
3-hydroxyphthalic anhydride (3HP)-modified bovine
beta-lactoglobulin (3HP-β-LG) is highly effective in inhibiting entry of pseudovirus (PsV) of high- and low-risk human papillomavirus (HPV) into the target cell. Intravaginally applied 3HP-β-LG-containing
vaginal gel could significantly inhibit
HPV infection and reduce viral load in the cervical region. However, we still do not understand the underlying molecular mechanism by which 3HP-β-LG is able to inhibit
HPV infection. Here, though, we showed that 3HP-β-LG did not inactivate HPV PsV, but rather blocked entry of HPV PsV into the target cell via its interaction with virus, not cell. It bound to the positively charged region in the HPV L1
protein, suggesting that 3HP-β-LG binds to HPV L1
protein through the interaction between the negatively charged region in 3HP-β-LG and the positively charged region in HPV L1
protein, thus competitively blocking the binding of HPV to the receptor on the basement membrane in vaginal mucosa. Although 3HP-modified chicken
ovalbumin (3HP-OVA) also carries high net negative charges, it exhibited no anti-HPV activity, suggesting that the interaction between 3HP-modified
protein and HPV L1
protein relies on both electrostatic and matchable conformation of the binding sites in both
proteins. When topically applied, 3HP-β-LG did not enter the host cell or blood circulation. These findings suggest that 3HP-β-LG targets HPV L1
protein and blocks HPV entry into the host cell, thus being safe and effective for topical application in the treatment of
HPV infection.