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

• Published in: The Journal of biological chemistry Vol. 287; no. 40; pp. 33503 - 33511
• Main Authors: Faingold, Omri, Cohen, Tomer, Shai, Yechiel
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 28.09.2012; American Society for Biochemistry and Molecular Biology
• Subjects: AIDS; Amino Acid Motifs; Amino Acid Sequence; Animals; Binding Sites; Biophysics; Biophysics - methods; Cell Line; Cell Proliferation; Computational Biology - methods; Fluorescence Resonance Energy Transfer; HIV Envelope Protein gp120 - chemistry; HIV Envelope Protein gp41 - chemistry; HIV-1; HIV-1 - chemistry; Humans; Immunosuppression; Immunosuppressive Agents - chemistry; Lipids - chemistry; Membrane Fusion; Membrane Proteins; Membrane Proteins - chemistry; Mice; Mice, Inbred C57BL; Molecular Biophysics; Molecular Sequence Data; Peptide Interactions; Protein Binding; Protein Conformation; Protein Interaction Mapping - methods; Protein Structure, Secondary; Protein Structure, Tertiary; Protein-Protein Interactions; Receptors, Antigen, T-Cell - immunology; Receptors, Antigen, T-Cell - metabolism; Sequence Homology, Amino Acid; T-Lymphocytes - cytology; T-Lymphocytes - metabolism; T-Lymphocytes - virology; HIV-1; Membrane Proteins; Immunosuppression; Membrane Fusion; AIDS; Biophysics; Peptide Interactions; Protein-Protein Interactions
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112.370817

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 (FP5–13), 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 FP5–13-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. Background: HIV utilizes its fusion peptide (FP) to both fuse and immunosuppress T-cells. Results: A conserved GxxxG-like motif within FP is critical for its function and structure. Conclusion: The GxxxG-like motif exerts its role via interaction with the transmembrane domain of TCRα. Significance: We shed light on the molecular mechanism of FP immunosuppressant activity and on the molecular recognition within the membrane milieu.