Folding of HIV‐1 Envelope glycoprotein involves extensive isomerization of disulfide bonds and conformation‐dependent leader peptide cleavage

Land, Aafke; Zonneveld, D.; Braakman, Ineke

doi:10.1096/fj.02-0811com

Cited by 98 publications

(149 citation statements)

References 55 publications

(61 reference statements)

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“…Devising an appropriate purification strategy may require a better understanding of the nature of nonfunctional Env. Our recent observations indicate that, contrary to popular perceptions, nonfunctional Env is not derived from trimer dissociation (19,20,36,69) but instead is a mostly static species that is coexpressed on particles alongside the trimer during synthesis. Nonfunctional…”

contrasting

confidence: 62%

HIV-1 Virus-Like Particles Bearing Pure Env Trimers Expose Neutralizing Epitopes but Occlude Nonneutralizing Epitopes

Tong

Crooks

Osawa

et al. 2012

J Virol

153

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Hypothetically, since native HIV-1 Env trimers are exclusively recognized by neutralizing antibodies, they might induce the neutralizing antibodies in a vaccine setting. This idea has not been evaluated due to the difficulty of separating trimers from nonfunctional Env (uncleaved gp160 and gp41 stumps). The latter are immunodominant and induce nonneutralizing antibodies. We previously showed that nonfunctional Env can be selectively cleared from virus-like particle (VLP) surfaces by enzyme digests (E. T. Crooks, T. Tong , K. Osawa, and J. M. Binley, J.Virol. 85:5825, 2011). Here, we investigated the effects of these digests on the antigenicity of VLPs and their sensitivity to neutralization. Before digestion, WT VLPs (bearing wild-type Env) and UNC VLPs (bearing uncleaved gp160) were recognized by various Env-specific monoclonal antibodies (MAbs), irrespective of their neutralizing activity, a result which is consistent with the presence of nonfunctional Env. After digestion, only neutralizing MAbs recognized WT VLPs, consistent with selective removal of nonfunctional Env (i.e., "trimer VLPs"). Digests eliminated the binding of all MAbs to UNC VLPs, again consistent with removal of nonfunctional Env. An exception was MAb 2F5, which weakly bound to digested UNC VLPs and bald VLPs (bearing no Env), perhaps due to lipid cross-reactivity. Trimer VLPs were infectious, and their neutralization sensitivity was largely comparable to that of undigested WT VLPs. However, they were ϳ100-fold more sensitive to the MAbs 4E10 and Z13e1, suggesting increased exposure of the gp41 base. Importantly, a scatterplot analysis revealed a strong correlation between MAb binding and neutralization of trimer VLPs. This suggests that trimer VLPs bear essentially pure native trimer that should allow its unfettered evaluation in a vaccine setting. Broadly neutralizing antibodies (bnAbs) are widely expected to be a crucial component of the immunity imparted by an effective HIV-1 vaccine (32, 42). These bnAbs neutralize the virus by being able to bind to native trimeric Envelope glycoprotein (Env) spikes on HIV-1 particle surfaces, thereby interfering with receptor engagement and infection (16,26,30,52). These Env spikes consist of trimers of gp120/gp41 heterodimers, in which gp120 is the surface subunit and gp41 is the transmembrane-anchoring subunit. By virtue of their compact and highly glycosylated nature, Env spikes effectively resist binding by all but a few rare neutralizing monoclonal antibodies (MAbs).To date, most Env-based vaccine candidates induce antibody responses against determinants that are inaccessible on native Env spikes and have therefore failed to induce meaningful neutralizing Ab responses (65). As the natural target of neutralizing Abs, the authentic Env spike in a native membrane context might fare better as an immunogen: logically, any antibodies induced by native Env trimers in a vaccine setting might be expected to neutralize. Most work in this area has centered on generating soluble Env trimers. However, the produ...

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contrasting

confidence: 62%

HIV-1 Virus-Like Particles Bearing Pure Env Trimers Expose Neutralizing Epitopes but Occlude Nonneutralizing Epitopes

Tong

Crooks

Osawa

et al. 2012

J Virol

153

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“…In light of the current interests regarding how different soluble (42), polytopic (50,51), or multisubunit (48,52) proteins fold in the ER, our work on DM demonstrates that two subunits of a heterodimeric complex can direct each others oxidative folding. We have shown that DM␤ chains require DM␣ chains to prevent misoxidation and conversely, DM␣ chains need DM␤ with the right disulfide bonds for proper oxidation of the DM complex.…”

Section: Discussionmentioning

confidence: 98%

The DMα and DMβ Chain Cooperate in the Oxidation and Folding of HLA-DM

Lith

Benham

2006

The Journal of Immunology

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HLA-DM (DM) is a heterodimeric MHC molecule that catalyzes the peptide loading of classical MHC class II molecules in the endosomal/lysosomal compartments of APCs. Although the function of DM is well-established, little is known about how DMα and β-chains fold, oxidize, and form a complex in the endoplasmic reticulum (ER). In this study, we show that glycosylation promotes, but is not essential for, DMαβ ER exit. However, glycosylation of DMα N15 is required for oxidation of the α-chain. The DMα and β-chains direct each others fate: single DMα chains cannot fully oxidize without DMβ, while DMβ forms disulfide-linked homodimers without DMα. Correct oxidation and subsequent ER egress depend on the unique DMβ C25 and C35 residues. This suggests that the C25-C35 disulfide bond in the peptide-binding domain overcomes the need for stabilizing peptides required by other MHC molecules.

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“…However, signal sequence cleavage for some proteins can also be a posttranslational event. For instance, the HIV envelope glycoprotein signal sequence is cleaved posttranslationally after the protein has folded to some degree (Li et al 1996;Land et al 2003). Tethering the amino-terminus to the membrane during the initial stages of folding appears to help direct the early folding and maturation processes; and because of this the timing of cleavage can be important.…”

Section: Signal Sequence Cleavagementioning

confidence: 99%

Protein Folding in the Endoplasmic Reticulum

Braakman

Hebert

2013

Cold Spring Harbor Perspectives in Biology

454

349

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In this article, we will cover the folding of proteins in the lumen of the endoplasmic reticulum (ER), including the role of three types of covalent modifications: signal peptide removal, Nlinked glycosylation, and disulfide bond formation, as well as the function and importance of resident ER folding factors. These folding factors consist of classical chaperones and their cochaperones, the carbohydrate-binding chaperones, and the folding catalysts of the PDI and proline cis -trans isomerase families. We will conclude with the perspective of the folding protein: a comparison of characteristics and folding and exit rates for proteins that travel through the ER as clients of the ER machinery.

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Folding of HIV‐1 Envelope glycoprotein involves extensive isomerization of disulfide bonds and conformation‐dependent leader peptide cleavage

Cited by 98 publications

References 55 publications

HIV-1 Virus-Like Particles Bearing Pure Env Trimers Expose Neutralizing Epitopes but Occlude Nonneutralizing Epitopes

HIV-1 Virus-Like Particles Bearing Pure Env Trimers Expose Neutralizing Epitopes but Occlude Nonneutralizing Epitopes

The DMα and DMβ Chain Cooperate in the Oxidation and Folding of HLA-DM

Protein Folding in the Endoplasmic Reticulum

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