HIV Fusion InhibitorsHIV Envelope Protein gp41HIV-1Peptide FragmentsVirus InternalizationMembrane FusionHIV InfectionsDrug Resistance, ViralCell FusionDrug DesignAnti-HIV AgentsPeptidesMolecular Sequence DataProtein Structure, SecondaryHIVAmino Acid SequenceViral Fusion ProteinsRecombinant Fusion Proteins