Abstract
The structure of BG505 gp140 SOSIP, a soluble mimic of the native HIV-1 envelope glycoprotein (Env), marks the beginning of new era in Env structure-based immunogen design. Displaying a well-ordered quaternary structure, these subtype A-derived trimers display an excellent antigenic profile, discriminating recognition by broadly neutralizing antibodies (bNAbs) from non-broadly neutralizing antibodies (non-bNAbs), and provide a solid Env-based immunogenic platform starting point. Even with this important advance, obtaining homogeneous well-ordered soluble SOSIP trimers derived from other subtypes remains challenging. Here, we report the “rescue” of homogeneous well-ordered subtype B and C SOSIP trimers from a heterogeneous Env mixture using CD4 binding site-directed (CD4bs) non-bNAbs in a negative-selection purification process. These non-bNAbs recognize the primary receptor CD4bs only on disordered trimers but not on the native Env spike or well-ordered soluble trimers due to steric hindrance. Following negative selection to remove disordered oligomers, we demonstrated recovery of well-ordered, homogeneous trimers by electron microscopy (EM). We obtained 3D EM reconstructions of unliganded trimers, as well as in complex with sCD4, a panel of CD4bs-directed bNAbs, and the cleavage-dependent, trimer-specific bNAb, PGT151. Using bio-layer light interferometry (BLI) we demonstrated that the well-ordered trimers were efficiently recognized by bNAbs and poorly recognized by non-bNAbs, representing soluble mimics of the native viral spike. Biophysical characterization was consistent with the thermostability of a homogeneous species that could be further stabilized by specific bNAbs. This study revealed that Env trimers generate different frequencies of well-ordered versus disordered aberrant trimers even when they are genetically identical. By negatively selecting the native-like well-ordered trimers, we establish a new means to obtain soluble Env mimetics derived from subtypes B and C for expanded use as candidate vaccine immunogens.
Highlights
The HIV-1 envelope glycoprotein (Env) is a trimer of heterodimers composed of two non-covalently associated subunits: the receptor-binding gp120 and the fusion machinery-containing gp41
We demonstrate that the JRFL and 16055 SOSIP trimers were purified to homogeneity by a novel means of isolation that utilizes non-broadly neutralizing antibodies (bNAbs) targeting the CD4 binding site-directed (CD4bs) in a negative-selection process that effectively separates well-ordered trimers from a mixture containing disordered aberrant trimers and other oligomeric states of Env
The JRFL and 16055 SOSIPs did form well-ordered trimers, but not as readily as the subtype A SOSIP trimers derived from the BG505 Env sequences [24,30], indicating molecular heterogeneity
Summary
The HIV-1 envelope glycoprotein (Env) is a trimer of heterodimers composed of two non-covalently associated subunits: the receptor-binding gp120 and the fusion machinery-containing gp. HIV-1 gp120 binds the CD4 molecule on the surface of human target T cells to initiate the viral entry process, and following co-receptor engagement, fusion is mediated by gp41 [2,3,4]. The surface-exposed HIV-1 Env trimer is the sole target for antibodies capable of neutralizing the virus [5]. A myriad of Env-directed broadly neutralizing antibodies (bNAbs) were isolated from numerous HIV-1-infected individuals, demonstrating that the human B cell response can effectively inhibit this variable pathogen [6,7,8,9,10,11]. Infection of macaques by a chimeric model virus, SHIV, can be prevented by Author Summary
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