title: A GxxxG-like motif within HIV-1 fusion peptide is critical to its immunosuppressant activity, structure, and interaction with the transmembrane domain of the T-cell receptor.
abstract: To thrive in the human body, HIV fuses to its target cell and evades the immune response via several mechanisms. The fusion cascade is initiated by the fusion peptide (FP), which is located at the N-terminal of gp41, the transmembrane protein of HIV. Recently, it has been shown that the HIV-1 FP, particularly its 5-13 amino acid region (FP(5-13)), suppresses T-cell activation and interacts with the transmembrane domain (TMD) of the T-cell receptor (TCR) complex. Specific amino acid motifs often contribute to such interactions in TMDs of membrane proteins. Using bioinformatics and experimental studies, we report on a GxxxG-like motif (AxxxG), which is conserved in the FP throughout different clades and strains of HIV-1. Biological activity studies and FTIR spectroscopy revealed that HIV FP(5-13)-derived peptides, in which the motif was altered either by randomization or by a single amino acid shift, lost their immunosuppressive activity concomitant with a loss of the β-sheet structure in a membranous environment. Furthermore, fluorescence studies revealed that the inactive mutants lost their ability to interact with their target site, namely, the TMD of TCRα, designated CP. Importantly, lipotechoic acid activated macrophages (lacking TCR) were not affected by FP, further demonstrating the specificity of the immunosuppressant activity of CP. Finally, although the AxxxG WT and the GxxxG analog both associated with the CP and immunosuppressed T-cells, the AxxxG WT but not the GxxxG analog induced lipid mixing. Overall, the data support an important role for the AxxxG motif in the function of FP and might explain the natural selection of the AxxxG motif rather than the classical GxxxG motif in FP.
authors.affiliation: Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Omri
authors.initials: O
authors.lastname: Faingold
authors.forename: Tomer
authors.initials: T
authors.lastname: Cohen
authors.forename: Yechiel
authors.initials: Y
authors.lastname: Shai
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001703:Biophysics / Q000379:methods; D002460:Cell Line; D049109:Cell Proliferation; D019295:Computational Biology / Q000379:methods; D031541:Fluorescence Resonance Energy Transfer; D015699:HIV Envelope Protein gp120 / Q000737:chemistry; D015700:HIV Envelope Protein gp41 / Q000737:chemistry; D015497:HIV-1 / Q000737:chemistry*; D006801:Humans; D007166:Immunosuppressive Agents / Q000737:chemistry; D008055:Lipids / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D025941:Protein Interaction Mapping / Q000379:methods; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011948:Receptors, Antigen, T-Cell / Q000276:immunology* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013601:T-Lymphocytes / Q000166:cytology / Q000378:metabolism / Q000821:virology*
chemical_list: D015699:HIV Envelope Protein gp120; D015700:HIV Envelope Protein gp41; D007166:Immunosuppressive Agents; D008055:Lipids; D008565:Membrane Proteins; D011948:Receptors, Antigen, T-Cell