Intramolecular interactions within the human immunodeficiency virus-1 gp41 loop region and their involvement in lipid merging.
The human immunodeficiency virus utilizes its gp41 fusion protein to mediate virus-cell membrane fusion. The conserved disulfide loop region in the gp41 hairpin conformation reverses the protein chain, such that the N-terminal heptad repeat and the C-terminal heptad repeat regions interact to form the six-helix bundle. Hence, it is conceivable that the sequential folded N- and C-terminal parts of the loop region also interact. We show that the N- and C-terminal parts of the loop preferably form disulfide-bonded heterodimers with slow oxidation kinetics. Furthermore, when the two parts were linked to a single polypeptide to form the full-length loop, only an intramolecular disulfide-bonded loop was formed. Fluorescence studies revealed that an interaction takes place between the N- and C-terminal parts of the loop in solution, which was sustained in membranes. Functionally, only a combination of the N- and C-loop parts induced lipid mixing of model liposomes, the level of which increased 8-fold when they were connected to a single polypeptide chain. In both cases, the activity was independent of the oxidation state of the cysteines. Overall, the data (i) provide evidence of a specific interaction between the N- and C-terminal parts of the loop, which can further stabilize gp41 hairpin conformation, and (ii) suggest that the interaction between the N- and C-terminal parts of the loop is sufficient to induce lipid merging without forming a disulfide bond.
Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, 76100 Israel.
Avraham
A
Ashkenazi
Elisa
E
Merklinger
Yechiel
Y
Shai
D000595:Amino Acid Sequence; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D015700:HIV Envelope Protein gp41 / Q000737:chemistry* / Q000378:metabolism*; D015658:HIV Infections / Q000821:virology*; D015497:HIV-1 / Q000737:chemistry / Q000502:physiology*; D054884:Host-Pathogen Interactions; D006801:Humans; D008081:Liposomes / Q000378:metabolism; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D053586:Virus Internalization
D004220:Disulfides; D015700:HIV Envelope Protein gp41; D008081:Liposomes; D003545:Cysteine