title: Solvent polarity-dependent structural refolding: a CD and NMR study of a 15 residue peptide.
abstract: A close association between the HIV surface protein gp120 and the CD4 T cell receptor initiates the viral multiplication cycle. A 15 amino acid peptide (LAV) within the CD4 binding domain of gp 120 has been shown to retain receptor binding ability. The structural behavior of the LAV peptide has been studied by CD and NMR methods in aqueous solution and upon addition of trifluoroethanol (TFE) to emulate the relatively apolar conditions at the membrane bound receptor. Previous work has shown that the LAV peptide folds into a beta-pleated structure in more polar buffer/TFE mixtures, while a concerted structural change can be observed at a concentration of 60% TFE (v/v). This abrupt, cooperative refolding from a regular beta-sheet to a helical secondary structure is known as "switch" behavior. Former CD experiments with LAV sequence variants have supported the assumption that four amino acids at the N-terminus (LPCR) are indispensable for the "switch." The tetrad has a strong beta-turn forming potential. The suggestion has been formulated that the tetrad can act as a nucleation site governing the refolding. The present NMR study of the LAV peptide in TFE gives evidence for a 3(10)-helix suggesting that the tetrad adopts a type III beta-turn and promotes the formation of a similar bend in the next overlapping tetrad until the sequence is restructured into a 3(10)-helix at a critical polarity favoring intrachain hydrogen bonds.
authors.affiliation: Department of Pathochemistry, German Cancer Research Center, Heidelberg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Graf von Stosch
authors.forename: M A
authors.initials: MA
authors.lastname: Jiménez
authors.forename: V
authors.initials: V
authors.lastname: Kinzel
authors.forename: J
authors.initials: J
authors.lastname: Reed
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D015704:CD4 Antigens / Q000378:metabolism; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002942:Circular Dichroism; D015699:HIV Envelope Protein gp120 / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry*; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012997:Solvents / Q000737:chemistry*; D014270:Trifluoroethanol / Q000737:chemistry
chemical_list: D015704:CD4 Antigens; D015699:HIV Envelope Protein gp120; D010446:Peptide Fragments; D012997:Solvents; D014270:Trifluoroethanol