Human APOBEC3F (hA3F) and APOBEC3G (hA3G) are antiretroviral cytidine deaminases that can be encapsidated during virus assembly to catalyze C3U deamination of the viral reverse transcripts in the next round of infection. Lentiviruses such as human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) have evolved the accessory protein Vif to induce their degradation before packaging. HIV type 1 (HIV-1) Vif counteracts hA3G but not rhesus macaque APOBEC3G (rhA3G) or African green monkey (AGM) APOBEC3G (agmA3G) because of a failure to bind the nonhuman primate proteins. The species specificity of the interaction is controlled by amino acid 128, which is aspartate in hA3G and lysine in rhA3G. With the objective of overcoming this species restriction, mutations were introduced into HIV-1 Vif at amino acid positions that differed in charge between HIV-1 Vif and SIV Vif. The mutant proteins were tested for the ability to counteract hA3G, rhA3G, and agmA3G. Alteration of the conserved sequence at positions 14 to 17 from DRMR to SERQ, which is the sequence in AGM Vif, caused HIV-1 Vif to functionally interact with rhA3G and agmA3G. Mutation of three residues to the sequence SEMQ allowed interaction with rhA3G. SEMQ Vif also counteracted D128K mutant hA3G and wild-type hA3G. Introduction of the sequence into an infectious molecular HIV-1 clone allowed the virus to replicate productively in human cells that expressed rhA3G or hA3G. These findings provide insight into the interaction of Vif with A3G and are a step toward the development of a novel primate model for AIDS.

L1 capsomeres purified from Escherichia coli represent an economic alternative to the recently launched virus-like particle (VLP)-based prophylactic vaccines against infection with human papillomavirus types 16 and 18 (HPV-16and HPV-18), which are causative agents of cervical cancer. It was recently reported that capsomeres are much less immunogenic than VLPs. Numerous modifications of the L1 protein leading to the formation of capsomeres but preventing capsid assembly have been described, such as the replacement of the cysteine residues that form capsid-stabilizing disulfide bonds or the deletion of helix 4. So far, the influence of these modifications on immunogenicity has not been thoroughly investigated. Here, we describe the purification of eight different HPV-16 L1 proteins as capsomeres from Escherichia coli. We compared them for yield, structure, and immunogenicity in mice. All L1 proteins formed almost identical pentameric structures yet differed strongly in their immunogenicity, especially regarding the humoral immune responses. Immunization of TLR4 ؊/؊ mice and DNA immunization by the same constructs confirmed that immunogenicity was independent of different degrees of contamination with copurifying immune-stimulatory molecules from E. coli. We hypothesize that immunogenicity correlates with the intrinsic ability of the capsomeres to assemble into larger particles, as only assembly-competent L1 proteins induced high antibody responses. One of the proteins (L1⌬N10) proved to be the most immunogenic, inducing antibody titers equivalent to those generated in response to VLPs. However, preassembly prior to injection did not increase immunogenicity. Our data suggest that certain L1 constructs can be used to produce highly immunogenic capsomeres in bacteria as economic alternatives to VLP-based formulations.Certain types of human papillomavirus (HPV) are the cause of cervical cancer, most frequently HPV types 16 and 18 (HPV-16 and HPV-18), which are responsible for about 50% and 20% of cases, respectively (8,15,16). Recently, two vaccines that prevent infection with HPV-16 and HPV-18 have been introduced to the market. These vaccines are based on the viral major structural protein L1, which can spontaneously self-assemble in vitro into empty virus-like particles (VLPs) that resemble the native virions in size and shape. VLPs have been shown to be highly immunogenic, as they can induce high titers of neutralizing antibodies (29,30). HPV virions and VLPs consist of 72 L1 pentamers, also called capsomeres, which are arranged in an icosahedral Tϭ7 particle lattice with a diameter of 55 nm. Cryo-electron microscopic analysis has revealed the presence of 60 hexavalent and 12 pentavalent capsomeres (4).Capsid assembly has been reported to be optimal at low pH (pH 5.4) and high ionic strength, whereas both high pH (pH 8.2) and the presence of reducing agents favor disassembly into capsomeres, the latter because the viral particles are stabilized by intercapsomeric disulfide bonds between two conserved cysteine resi...

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