Recombinant trimeric mimics of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) spike should expose as many epitopes as possible for broadly neutralizing antibodies (bNAbs) but few, if any, for nonneutralizing antibodies (non-NAbs). Soluble, cleaved SOSIP.664 gp140 trimers based on the subtype A strain BG505 approach this ideal and are therefore plausible vaccine candidates. Here, we report on the production and in vitro properties of a new SOSIP.664 trimer derived from a subtype B env gene, B41, including how to make this protein in low-serum media without proteolytic damage (clipping) to the V3 region. We also show that nonclipped trimers can be purified successfully via a positive-selection affinity column using the bNAb PGT145, which recognizes a quaternary structure-dependent epitope at the trimer apex. Negative-stain electron microscopy imaging shows that the purified, nonclipped, native-like B41 SOSIP.
IMPORTANCEThe cleaved, trimeric envelope protein complex is the only neutralizing antibody target on the HIV-1 surface. Many vaccine strategies are based on inducing neutralizing antibodies. For HIV-1, one approach involves using recombinant, soluble protein mimics of the native trimer. At present, the only reliable way to make native-like, soluble trimers in practical amounts is via the introduction of specific sequence changes that confer stability on the cleaved form of Env. The resulting proteins are known as SOSIP.664 gp140 trimers, and the current paradigm is based on the BG505 subtype A env gene. Here, we describe the production and characterization of a SOSIP.664 protein derived from a subtype B gene (B41), together with a simple, one-step method to purify native-like trimers by affinity chromatography with a trimer-specific bNAb, PGT145. The resulting trimers will be useful for structural and immunogenicity experiments aimed at devising ways to make an effective HIV-1 vaccine.
Immunogens capable of inducing protective titers of broadly neutralizing antibodies (bNAbs) are being widely sought for use in vaccine design strategies for human immunodeficiency virus type 1 (HIV-1) (1). The basis of this approach is that bNAbs can prevent globally diverse HIV-1 strains from infecting target cells. They do so via binding to the envelope glycoprotein (Env) complex on the virion surface, an event that is both necessary and sufficient to neutralize HIV-1 infectivity (2, 3). One of the more common strategies to induce bNAbs involves the design of soluble, recombinant protein mimics of the native Env complex, a meta-stable structure comprising three gp120 and three gp41 subunits. The production of soluble Env trimers involves introducing a stop codon to truncate the gp41 ectodomain (gp41 ECTO ) subunit prior to the transmembrane region to yield soluble gp140 proteins (4-6). The fragility of the Env complex is, however, a substantial problem from a protein engineering perspective, as the natural noncovalent interactions between the six subunits are not robust enough to allow so...