title: NMR and circular dichroism studies on the conformation of a 44-mer peptide from a CD4-binding domain of human immunodeficiency virus envelope glycoprotein.
abstract: Two-dimensional NMR, circular dichroism (CD) experiments and molecular modeling were performed to study the secondary structure of a 44-mer peptide fragment derived from the C4 region of gp120 of human immunodeficiency virus in aqueous solution. It was found a nascent helical structure exists following a type I turn near the N-terminus of the peptide. The proline residue in the turn appears to serve as a helix initiator. The helical structure was in fast dynamic equilibrium with beta- or random coil form on the NMR scale. A reverse turn was identified at a section containing two consecutive proline residues. A nascent helical structure has been detected for the region near the C-terminus of the 44-mer peptide. Higher helical content for the peptide is also indicated by CD studies on TFE titration. Thus it is proposed that, in more apolar medium, the Pro-Pro turn and the segment amino-terminal to it, spanning about 20 amino acids, may be converted into helix structure. Moreover, the region near the C-terminus of the peptide may also be induced into helix, so that a helix-turn-helix structure may be formed in the C4 domain of gp120. A helical wheel representation of this stretch shows amphipathicity of the helix. The biological implication of the conformational adaptibility of the peptide was discussed.
authors.affiliation: Institute of Chemistry, Academia Sinica, Taipei, Taiwan, Republic of China. dkc@chem.sinica.edu.tw
authors.forename: D K
authors.initials: DK
authors.lastname: Chang
authors.forename: W J
authors.initials: WJ
authors.lastname: Chien
authors.forename: S F
authors.initials: SF
authors.lastname: Cheng
authors.forename: S T
authors.initials: ST
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000502:physiology; D001665:Binding Sites; D015704:CD4 Antigens / Q000502:physiology*; D002942:Circular Dichroism; D015699:HIV Envelope Protein gp120 / Q000737:chemistry* / Q000378:metabolism; D015497:HIV-1 / Q000502:physiology*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation
chemical_list: D015703:Antigens, CD; D015704:CD4 Antigens; D015699:HIV Envelope Protein gp120; D010446:Peptide Fragments