The FLG Motif in the N‐Terminal Region of Glucoprotein 41 of Human Immunodeficiency Virus Type 1 Adopts a Type‐I β Turn in Aqueous Solution and Serves as the Initiaion Site for Helix Formation

Abstract

NMR and CD studies were carried out on a peptide representing the hydrophobic N-terminal domain of envelope glycoprotein of human immunodeficiency virus type-1 in solutions of varying polarity. It was found that in aquaeous solution the amide proton of glycine in the FLG motif resonated at a considerably high field and its chemical shift, within the limit of experimental precision, had a temperature coefficient of zero in the range studied. The upfield shift of NH of the glycine could be largely attributed to the ring-current effect of phenylalanine in the FLG motif that participated in a type-1 /3 turn with a short CP(i)-NH(i+2) distance. The slower proton-deuterion exchange for the glycine amide proton relative to that of other glycines was consistent with a folded structure for the motif in aquaeous solution. Results of the molecular simulation showed that this proton was shielded from the solvent by non-polar side chains of the amino acid residues surrounding the turn stabilized by hydrophobic interactions, thus explaining the zero temperature coefficient of the proton chemical shift. The structural stabilizing effect of the hydrophobic interaction was supported by the behavior of the proton in less polar Me,SO solution, in which the anomaly in the chemical shift and its temperature coefficient was less prominent. Detailed secondary-structure analysis suggested that the / 3 turn of the FLG motif may act as an initiation core for helix formation, probably because the turn readily transforms into helical form. Keywords:type-] fi turn ; initiation site; hydrophobic interaction ; ring-current shielding.In the elucidation of the mechanism of protein folding, the identification of the initiation site and of the force that stabilizes the structure are of importance (Baldwin, 1989;Dyson et al., 1988). Secondary structure formation in localized regions at the early stage of folding is an essential element in, for instance, the framework and molten-globule models (Anfinsen, 1972; Dolgikh et al., 1981;Kim and Baldwin, 1982). Hydrophobic interaction (Eisenberg et al., 1986; Tanford, 1980: Nemethy andScheraga, 1962) and hydrogen bonds (Zimm and Bragg, 1959) have been considered as driving forces for the formation of reverse turns and short segments of helix. The electrostatic (or ionic) attraction probably also plays a role in stabilizing initial structural elements in special cases (Wlodawer and Sjolin, 1983).For helices, higher free energy is required for nucleation, i.e. forming the first and the second hydrogen bonds between amide and carbonyl groups on the backbone of protein chain, because of the larger decrease in entropy. The enthalpic gain is greatly reduced since these hydrogen bonds have to compete with the solvent, i.e. water, molecules, which have excellent capacity to form hydrogen bonds. The unfavorable free energy of helix nucleation is manifested in the generally small values of the parameter CJ for amino acids in the Zimm-Bragg formalism for helixcoil transition (Zimm and Bragg, 1959). Thus, propagation...

Structure and membrane interaction of the internal fusion peptide of avian sarcoma leukosis virus

“…In contrast, helical structures are greatly enhanced in the membranous environment for both the N-terminal and internal FPs of class I fusion proteins as they are transferred from aqueous medium with a b-turn in the middle of the sequence, as suggested in the present work ( Fig. 7) and for gp41 fusion peptide [12]. Furthermore, the core structure of the class I fusion proteins, which also undergoes structural rearrangement on transition to the fusogenic state, is predominantly helical in both pre-and postfusion states.…”

“…In the following, a variety of physical properties of the putative IFP of ASLV are reported and differences between N‐terminal and internal FP are compared. The pH dependence of some of the properties is discussed in regard to the experimental observation that ASLV induced hemifusion, but not complete fusion, at neutral pH [12].…”

Fusion Peptides and Transmembrane Domains of Fusion Proteins are Characterized by Different but Specific Structural Properties

“…The results for these fusion peptides are in agreement with the experiments of other groups that analyzed the secondary structure of these FPs under related conditions 21. 31–34 The detected structural flexibility can be assigned to the greater abundance of glycine and alanine in the fusion peptide sequence. Mutational analyses have shown that distinct glycine residues (Gly1, Gly4 and Gly8 of HA2 FP; Gly10 and Gly13 of HIV‐1 FP) are critical for fusion activity 35.…”

Membrane-Perturbing Domains of HIV Type 1 Glycoprotein 41

“…8A) may be due to the Nterminal HIV-1 gp41 peptide forming filamentous, aggregated structures in aqueous medium. 38 The absence of a-helical structure in FP-I suspended in aqueous media has, however, been independently confirmed in nuclear magnetic resonance (NMR) 80 and Fourier transform infrared (FTIR) studies. 84 One mechanism by which DP-178 might inhibit the membrane perturbations induced by either DP-107 or FP-I (Figs.…”

“…Circular dichroism (CD) spectroscopy has been extensively used to determine the secondary structure of synthetic HIV-1 gp41 peptides in either aqueous 3,[16][17][18]21,22,24,37,46,59,79,80 or structure-promoting 17,21-24,37,38,48,51,58-60,79-83 (e.g., lipid) environments. Here, CD spectroscopic analysis of FP-I, DP-107, and DP-178 in PBS buffer should indicate the conformational state of these gp41 peptides as they are presented to the membrane.…”