Abstract
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. Simultaneously, the signal peptide delays folding by tethering the N terminus to the membrane, until assembly with the Cterminus. Second, its carefully timed cleavage represents intramolecular quality control and ensures release of (only) natively folded gp120. Postponed cleavage and the redox-active cysteine are both highly conserved and important for viral fitness. Considering the ∼15% proteins with signal peptides and the frequency of N-to-C contacts in protein structures, these regulatory roles of signal peptides are bound to be more common in secretory-protein biogenesis.
Highlights
The endoplasmic reticulum (ER) is home to a wealth of resident chaperones and folding enzymes that cater to roughly a third of all mammalian proteins during their biosynthesis (Ellgaard et al, 2016; Kanapin et al, 2003)
Gp120 undergoes extensive disulfide isomerization during folding, as seen from the smear of gp120 folding intermediates (ITs) in the non-reducing (NR) gel upon 35S-radiolabeling, from reduced gp120 down to beyond NT gp120 (Land et al, 2003; Figure 1B, NR, 0ʹ chase). This smear disappears into a NT band with discrete mobility at around the time the signal peptide is removed (Figure 1B, R, from 150 chase)
Radioactive pulse-chase experiments showed that only full-length gp120 (511 residues) and 494X lost their signal peptides
Summary
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. The signal peptide improves folding fidelity by enhancing conformational plasticity of gp120 by driving disulfide isomerization through a redox-active cysteine. The signal peptide delays folding by tethering the N terminus to the membrane, until assembly with the C terminus. Its carefully timed cleavage represents intramolecular quality control and ensures release of (only) natively folded gp120. Postponed cleavage and the redox-active cysteine are both highly conserved and important for viral fitness. Considering the $15% proteins with signal peptides and the frequency of N-to-C contacts in protein structures, these regulatory roles of signal peptides are bound to be more common in secretory-protein biogenesis
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
