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Crystal structure of HIV-1 gp41 including both fusion peptide and membrane proximal external regions.

Buzon V, Natrajan G, Schibli D, Campelo F, Kozlov MM, Weissenhorn W - PLoS Pathog. (2010)

Bottom Line: We calculate that this structural motif might facilitate the generation of membrane curvature on the viral membrane.The presence of FPPR and MPER increases the melting temperature of gp41 significantly in comparison to the core structure of gp41.Furthermore, we provide the first structural evidence that part of MPER will be membrane inserted within trimeric gp41.

View Article: PubMed Central - PubMed

Affiliation: Unit of Virus Host Cell Interactions UMI 3265, Université Joseph Fourier-EMBL-CNRS, Grenoble, France.

ABSTRACT
The HIV-1 envelope glycoprotein (Env) composed of the receptor binding domain gp120 and the fusion protein subunit gp41 catalyzes virus entry and is a major target for therapeutic intervention and for neutralizing antibodies. Env interactions with cellular receptors trigger refolding of gp41, which induces close apposition of viral and cellular membranes leading to membrane fusion. The energy released during refolding is used to overcome the kinetic barrier and drives the fusion reaction. Here, we report the crystal structure at 2 A resolution of the complete extracellular domain of gp41 lacking the fusion peptide and the cystein-linked loop. Both the fusion peptide proximal region (FPPR) and the membrane proximal external region (MPER) form helical extensions from the gp41 six-helical bundle core structure. The lack of regular coiled-coil interactions within FPPR and MPER splay this end of the structure apart while positioning the fusion peptide towards the outside of the six-helical bundle and exposing conserved hydrophobic MPER residues. Unexpectedly, the section of the MPER, which is juxtaposed to the transmembrane region (TMR), bends in a 90 degrees-angle sideward positioning three aromatic side chains per monomer for membrane insertion. We calculate that this structural motif might facilitate the generation of membrane curvature on the viral membrane. The presence of FPPR and MPER increases the melting temperature of gp41 significantly in comparison to the core structure of gp41. Thus, our data indicate that the ordered assembly of FPPR and MPER beyond the core contributes energy to the membrane fusion reaction. Furthermore, we provide the first structural evidence that part of MPER will be membrane inserted within trimeric gp41. We propose that this framework has important implications for membrane bending on the viral membrane, which is required for fusion and could provide a platform for epitope and lipid bilayer recognition for broadly neutralizing gp41 antibodies.

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Related in: MedlinePlus

The FPPR-MPER regions are splayed apart.A) Close-up view from the bottom showing residue Leu 545 as the last coiled coil interacting residue of the HR1 core of gp41. The preceding potential heptad positions are Ala 541 and Thr 538. B) Close up view revealing mostly hydrophobic interactions between FPPR and MPER and only one hydrogen bond between the carbonyl of Ala and NE1 of Trp 670. C) Close-up of solvent exposed hydrophobic MPER residues.
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ppat-1000880-g003: The FPPR-MPER regions are splayed apart.A) Close-up view from the bottom showing residue Leu 545 as the last coiled coil interacting residue of the HR1 core of gp41. The preceding potential heptad positions are Ala 541 and Thr 538. B) Close up view revealing mostly hydrophobic interactions between FPPR and MPER and only one hydrogen bond between the carbonyl of Ala and NE1 of Trp 670. C) Close-up of solvent exposed hydrophobic MPER residues.

Mentions: Both FPPR and MPER extend HR1 and HR2 as continuous helices, but neither extension shows the regular knobs into holes packing reminiscent of classical coiled coils. Instead the FPPR region splays the inner core apart starting from Leu 545 (a position) (Fig. 3A). The distance between Arg 579 residues at the HR1 C-terminus is 12.5 Å while the one at the extreme N-terminus opens up to 22.7 Å (between Gly residues 531). As a consequence HR1 heptad positions are too far apart for interaction (Fig. 3A). The FPPR-MPER region is only stabilized by few hydrophobic contacts between adjacent chains, including interactions of Gly 531- Leu679, Ala 533- Trp 670, Met 535-Ile 675/Asn 671, Thr 536/Leu 537 - Trp 666 and one hydrogen bond between the carbonyl of Ala 533 and NE1 of Trp 670 (Fig. 3B). At position of MPER residue Asn 676, the N-terminus of FPPR-HR1 points towards the outside of the rod (Fig. 2A) facilitating fusion peptide (residues 512–530) membrane interaction or further refolding of FP with MPER and possibly TMR. Another striking feature of the structure is the solvent exposure of a stretch of hydrophobic MPER residues (Trp 666, Leu 669, Trp670, Trp 672, Phe 673) that generate a hydrophobic surface patch (Fig. S5).


Crystal structure of HIV-1 gp41 including both fusion peptide and membrane proximal external regions.

Buzon V, Natrajan G, Schibli D, Campelo F, Kozlov MM, Weissenhorn W - PLoS Pathog. (2010)

The FPPR-MPER regions are splayed apart.A) Close-up view from the bottom showing residue Leu 545 as the last coiled coil interacting residue of the HR1 core of gp41. The preceding potential heptad positions are Ala 541 and Thr 538. B) Close up view revealing mostly hydrophobic interactions between FPPR and MPER and only one hydrogen bond between the carbonyl of Ala and NE1 of Trp 670. C) Close-up of solvent exposed hydrophobic MPER residues.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2865522&req=5

ppat-1000880-g003: The FPPR-MPER regions are splayed apart.A) Close-up view from the bottom showing residue Leu 545 as the last coiled coil interacting residue of the HR1 core of gp41. The preceding potential heptad positions are Ala 541 and Thr 538. B) Close up view revealing mostly hydrophobic interactions between FPPR and MPER and only one hydrogen bond between the carbonyl of Ala and NE1 of Trp 670. C) Close-up of solvent exposed hydrophobic MPER residues.
Mentions: Both FPPR and MPER extend HR1 and HR2 as continuous helices, but neither extension shows the regular knobs into holes packing reminiscent of classical coiled coils. Instead the FPPR region splays the inner core apart starting from Leu 545 (a position) (Fig. 3A). The distance between Arg 579 residues at the HR1 C-terminus is 12.5 Å while the one at the extreme N-terminus opens up to 22.7 Å (between Gly residues 531). As a consequence HR1 heptad positions are too far apart for interaction (Fig. 3A). The FPPR-MPER region is only stabilized by few hydrophobic contacts between adjacent chains, including interactions of Gly 531- Leu679, Ala 533- Trp 670, Met 535-Ile 675/Asn 671, Thr 536/Leu 537 - Trp 666 and one hydrogen bond between the carbonyl of Ala 533 and NE1 of Trp 670 (Fig. 3B). At position of MPER residue Asn 676, the N-terminus of FPPR-HR1 points towards the outside of the rod (Fig. 2A) facilitating fusion peptide (residues 512–530) membrane interaction or further refolding of FP with MPER and possibly TMR. Another striking feature of the structure is the solvent exposure of a stretch of hydrophobic MPER residues (Trp 666, Leu 669, Trp670, Trp 672, Phe 673) that generate a hydrophobic surface patch (Fig. S5).

Bottom Line: We calculate that this structural motif might facilitate the generation of membrane curvature on the viral membrane.The presence of FPPR and MPER increases the melting temperature of gp41 significantly in comparison to the core structure of gp41.Furthermore, we provide the first structural evidence that part of MPER will be membrane inserted within trimeric gp41.

View Article: PubMed Central - PubMed

Affiliation: Unit of Virus Host Cell Interactions UMI 3265, Université Joseph Fourier-EMBL-CNRS, Grenoble, France.

ABSTRACT
The HIV-1 envelope glycoprotein (Env) composed of the receptor binding domain gp120 and the fusion protein subunit gp41 catalyzes virus entry and is a major target for therapeutic intervention and for neutralizing antibodies. Env interactions with cellular receptors trigger refolding of gp41, which induces close apposition of viral and cellular membranes leading to membrane fusion. The energy released during refolding is used to overcome the kinetic barrier and drives the fusion reaction. Here, we report the crystal structure at 2 A resolution of the complete extracellular domain of gp41 lacking the fusion peptide and the cystein-linked loop. Both the fusion peptide proximal region (FPPR) and the membrane proximal external region (MPER) form helical extensions from the gp41 six-helical bundle core structure. The lack of regular coiled-coil interactions within FPPR and MPER splay this end of the structure apart while positioning the fusion peptide towards the outside of the six-helical bundle and exposing conserved hydrophobic MPER residues. Unexpectedly, the section of the MPER, which is juxtaposed to the transmembrane region (TMR), bends in a 90 degrees-angle sideward positioning three aromatic side chains per monomer for membrane insertion. We calculate that this structural motif might facilitate the generation of membrane curvature on the viral membrane. The presence of FPPR and MPER increases the melting temperature of gp41 significantly in comparison to the core structure of gp41. Thus, our data indicate that the ordered assembly of FPPR and MPER beyond the core contributes energy to the membrane fusion reaction. Furthermore, we provide the first structural evidence that part of MPER will be membrane inserted within trimeric gp41. We propose that this framework has important implications for membrane bending on the viral membrane, which is required for fusion and could provide a platform for epitope and lipid bilayer recognition for broadly neutralizing gp41 antibodies.

Show MeSH
Related in: MedlinePlus