The fraction that is not recovered using acidic pH was eluted using freshly made 100 mM Triethylamine buffer at pH 11.5. One set of neutralization assays was performed using an AA-2 cell and infectious virus (HIV-1 IIIB) as described previously [5]. MeOH:CHCl3:H2O, and subjected to the RDX same procedure described above. LipidCTL designates the only lipid control.(TIFF) pone.0052740.s001.tif (721K) GUID:?E172D6EB-41ED-4F76-8BBA-FE2B4962D965 Figure S2: Membrane-bound MAb2F5 particles as detected by cryo-TEM. Micrographs correspond to LUV pre-incubated with MPERp:FPp mixture and antibody as indicated in the caption for Figure 6 (left panel). Arrows point to rods protruding from the membrane surface. The scale bar represents 100 nm.(TIFF) pone.0052740.s002.tif (470K) GUID:?3586618A-31E4-437E-A99D-06FFA35E6003 Figure S3: MAb2F5-induced effects on MPERp/FPp-containing lipid vesicle morphology. Micrographs correspond to LUV pre-incubated with MPERp:FPp mixture and antibody as indicated in the caption for Figure 6 (right panel). A) The fields show vesicle aggregation induced by the antibody. Tubular structures and apparent loss of the bilayer integrity (open vesicles) can be observed at some points. The scale bar represents 100 nm. BCF) Antibody particles (indicated by arrows and asterisks) concentrated at the surface NS13001 of vesicles that displayed morphologies consistent with loss of bilayer integrity (red dotted lines) and membrane evagination (blue bilayers).(PDF) pone.0052740.s003.pdf (4.4M) GUID:?B8E1BAB0-4C25-4B54-9069-D6A93ABF5D59 Figure S4: Immunogenicity of membrane-bound peptides. A) Sera obtained from two rabbits (59 and 60) immunized with membrane-bound MPERp/FPp were titrated in ELISA using the MPERp/FPp mixture (1.4 M of each peptide). Black symbols represent the respective pre-immune sera. B) Cross-reactivity of the sera to 1 1.4 MPERp (black), rec-gp41 (blue), 2F5ep (green), preTM (red) and C34 (brown) immobilized in ELISA plates.(TIF) pone.0052740.s004.tif (351K) GUID:?9C3C2F9B-3F6F-451C-8B4C-E072AE991D53 Figure S5: Evidence for specific structures adopted by membrane-bound MPERp/FPp NS13001 complexes. A) Left: Circular dichroism (CD) spectra of the MPERp:FPp mixture in the presence of POPC:Chol vesicles. The panel displays the comparison of the experimental spectrum (solid line) and the spectrum calculated for the addition of non-interacting peptide signals (dotted line). The significant differences between these spectra are consistent with a conformational rearrangement of the MPERp:FPp mixtures upon contact with vesicles. Right: comparable experimental spectra were measured for the complex (solid line) in the presence of 5% of the structure-promoting HFIP. Previous structural characterization of HybK3, a hybrid peptide combining FP and 2F5 epitope sequences, indicated that conformers containing high proportion of type I -turns could give rise to this kind of CD spectra [22]. To illustrate this point the CD spectrum of HybK3 is displayed in the same panel (dashed line). B) Left: the experimental and calculated spectra for MPERp:FPp mixtures coincided in dodecylphosphocholine (DPC) micelles. These spectra were compatible with the adoption of main -helical conformations by each peptide. Right: comparable spectra could also be recovered in the low-polarity medium provided by 25% HFIP. C) Cross-linking assays. Cross-linking was much more effective if the peptides were stored with vesicles (left panel), than if they were solubilized by DPC (right panel).(PDF) pone.0052740.s005.pdf (358K) GUID:?DDF99BD2-425E-4525-A865-73CF368D3F3A Figure S6: Recovery from rabbit serum of antibodies targeting MPERp/FPp complex on vesicle surfaces. A) Peptide recognition by rabbit IgG purified with MPERp/FPp-Cys17 adsorbed onto vesicle surfaces. Recovered antibodies were titrated by ELISA against the following peptides: FPp (blue); C34 (orange); MPERp (red); CpreTM (green); TMDp (black). Reactivity to 2F5ep is denoted by empty red symbols and dotted line. B) Neutralization assays with rabbit IgG purified with 2F5ep-Cys or MPERp/FPp-Cys17 on vesicles (red and blue symbols, respectively). In these assays, HXB2-env pseudoviruses were pre-incubated with antibodies, and infection of TZM-bl target cells subsequently monitored by flow cytometry as previously described [35], [38]. Plotted infection percentage values NS13001 are means of two experimental determinations.(TIFF) pone.0052740.s006.tiff (527K) GUID:?18CDD88B-E37F-480D-BBD5-37A344654CF3 Abstract The membrane proximal external region (MPER) of the fusogenic HIV-1 glycoprotein-41 harbors the epitope sequence recognized by 2F5, a NS13001 broadly neutralizing antibody isolated from an infected individual. Structural mimicry of the conserved MPER 2F5 epitope constitutes a pursued goal in the field of anti-HIV vaccine development. It has been proposed that 2F5 epitope folding into its native state is attained in the vicinity of the membrane interface and might involve interactions with other viral structures. Here we present results indicating that oligomeric complexes established between MPER and the conserved amino-terminal fusion peptide (FP) can partition into lipid vesicles and be specifically bound by the 2F5 antibody at their surfaces. Cryo-transmission electron microscopy of liposomes doped with MPER:FP peptide mixtures provided the structural grounds for complex recognition by antibody at lipid bilayer surfaces. Supporting the immunogenicity of the membrane-bound complex, these MPER:FP peptide-vesicle formulations could trigger cross-reactive anti-MPER antibodies in rabbits. Thus, our observations suggest that contacts with N-terminal regions of gp41 may stabilize the 2F5 epitope as a membrane-surface antigen..