title: On the interaction between gp41 and membranes: the immunodominant loop stabilizes gp41 helical hairpin conformation.
abstract: gp41 is the protein responsible for the process of membrane fusion that allows primate lentiviruses (HIV and SIV) to enter into their host cells. gp41 ectodomain contains an N-terminal and a C-terminal heptad repeat region (NHR and CHR) connected by an immunodominant loop. In the absence of membranes, the NHR and CHR segments fold into a protease-resistant core with a trimeric helical hairpin structure. However, when the immunodominant loop is not present (either in a complex formed by HIV-1 gp41-derived NHR and CHR peptides or by mild treatment with protease of recombinant constructs of HIV-1 gp41 ectodomain, which also lack the N-terminal fusion peptide and the C-terminal Trp-rich region) membrane binding induces a conformational change in the gp41 core structure. Here, we further investigated whether covalently linking the NHR and CHR segments by the immunodominant loop affects this conformational change. Specifically, we analyzed a construct corresponding to a fragment of SIVmac239 gp41ectodomain (residues 27-149, named e-gp41) by means of surface plasmon resonance, Trp and rhodamine fluorescence, ATR-FTIR spectroscopy, and differential scanning calorimetry. Our results suggest that the presence of the loop stabilizes the trimeric helical hairpin both when e-gp41 is in aqueous solution and when it is bound to the membrane surface. Bearing in mind possible differences between HIV-1 and SIV gp41, and considering that the gp41 ectodomain constructs analyzed to date lack the N-terminal fusion peptide and the C-terminal Trp-rich region, we discuss our observations in relation to the mechanism of virus-induced membrane fusion.
authors.affiliation: Department of Biological Chemistry, Weizmann Institute of Science, 76100, Rehovot, Israel.
authors.forename: Sergio G
authors.initials: SG
authors.lastname: Peisajovich
authors.forename: Lior
authors.initials: L
authors.lastname: Blank
authors.forename: Raquel F
authors.initials: RF
authors.lastname: Epand
authors.forename: Richard M
authors.initials: RM
authors.lastname: Epand
authors.forename: Yechiel
authors.initials: Y
authors.lastname: Shai
mesh_terms: D002152:Calorimetry, Differential Scanning; D002462:Cell Membrane / Q000502:physiology*; D002942:Circular Dichroism; D003545:Cysteine / Q000737:chemistry; D005453:Fluorescence; D006358:Hot Temperature; D006801:Humans; D016056:Immunodominant Epitopes / Q000737:chemistry* / Q000378:metabolism; D008081:Liposomes; D008561:Membrane Fusion; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D012191:Retroviridae Proteins / Q000737:chemistry* / Q000378:metabolism; D012235:Rhodamines / Q000737:chemistry / Q000378:metabolism; D015302:Simian Immunodeficiency Virus / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared; D020349:Surface Plasmon Resonance; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D016056:Immunodominant Epitopes; D008081:Liposomes; D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D012191:Retroviridae Proteins; D012235:Rhodamines; C082614:SIV envelope protein gp41; D014364:Tryptophan; D003545:Cysteine