Intramolecular quality control: HIV-1 envelope gp160 signal-peptide cleavage as a functional folding checkpoint.

Removal of the membrane-tethering signal peptides that target secretory proteins to the endoplasmic reticulum is a prerequisite for proper folding. While generally thought to be removed co-translationally, we report two additional post-targeting functions for the HIV-1 gp120 signal peptide, which remains attached until gp120 folding triggers its removal. First, the signal peptide improves folding fidelity by enhancing conformational plasticity of gp120 by driving disulfide isomerization through a redox-active cysteine.

Structure and topology around the cleavage site regulate post-translational cleavage of the HIV-1 gp160 signal peptide.

Like all other secretory proteins, the HIV-1 envelope glycoprotein gp160 is targeted to the endoplasmic reticulum (ER) by its signal peptide during synthesis. Proper gp160 folding in the ER requires core glycosylation, disulfide-bond formation and proline isomerization. Signal-peptide cleavage occurs only late after gp160 chain termination and is dependent on folding of the soluble subunit gp120 to a near-native conformation.

Optimization of human immunodeficiency virus type 1 envelope glycoproteins with V1/V2 deleted, using virus evolution.

The human immunodeficiency virus type 1 envelope glycoprotein (Env) complex is the principal focus of neutralizing antibody-based vaccines. The functional Env complex is a trimer consisting of six individual subunits: three gp120 molecules and three gp41 molecules. The individual subunits have proven unsuccessful as vaccines presumably because they do not resemble the functional Env complex.

Evolution rescues folding of human immunodeficiency virus-1 envelope glycoprotein GP120 lacking a conserved disulfide bond.

The majority of eukaryotic secretory and membrane proteins contain disulfide bonds, which are strongly conserved within protein families because of their crucial role in folding or function. The exact role of these disulfide bonds during folding is unclear. Using virus-driven evolution we generated a viral glycoprotein variant, which is functional despite the lack of an absolutely conserved disulfide bond that links two antiparallel beta-strands in a six-stranded beta-barrel.

Only five of 10 strictly conserved disulfide bonds are essential for folding and eight for function of the HIV-1 envelope glycoprotein.

Protein folding in the endoplasmic reticulum goes hand in hand with disulfide bond formation, and disulfide bonds are considered key structural elements for a protein's folding and function. We used the HIV-1 Envelope glycoprotein to examine in detail the importance of its 10 completely conserved disulfide bonds. We systematically mutated the cysteines in its ectodomain, assayed the mutants for oxidative folding, transport, and incorporation into the virus, and tested fitness of mutant viruses.

Folding of HIV-1 envelope glycoprotein involves extensive isomerization of disulfide bonds and conformation-dependent leader peptide cleavage.

Human immunodeficiency virus binds and enters cells via the Envelope glycoprotein gp160 at its surface. In infected cells, gp160 is found not only on the plasma membrane but also in the endoplasmic reticulum (ER). Our aim was to establish rate-determining steps in the maturation process of gp160, using a radioactive pulse-chase approach.