Structural and Functional Roles of HIV-1 gp41 Pretransmembrane Sequence Segmentation

Abstract

The membrane-proximal segment connecting the helical core with the transmembrane anchor of human immunodeficiency virus type 1 gp41 is accessible to broadly neutralizing antibodies and plays a crucial role in fusion activity. New predictive approaches including computation of interfacial affinity and the corresponding hydrophobic moments suggest that this region is functionally segmented into two consecutive subdomains: one amphipathic at the N-terminal side and one fully interfacial at the C-terminus. The N-terminal subdomain would extend alpha-helices from the preceding carboxy-terminal heptad repeat and provide, at the same time, a hydrophobic-at-interface surface. Experiments were performed to compare a wild-type representing pretransmembrane peptide with a nonamphipathic defective sequence, which otherwise conserved interfacial hydrophobicity at the carboxy-subdomain. Results confirmed that both penetrated equally well into lipid monolayers and both were able to partition into membrane interfaces. However only the functional sequence: 1), adopted helical structures in solution and in membranes; 2), formed homo-oligomers in solution and membranes; and 3), inhibited gp41-induced cell-cell fusion. These data support two roles for gp41 aromatic-rich pretransmembrane sequence: 1), oligomerization of gp41; and 2), immersion into the viral membrane interface. Accessibility to membrane interfaces and subsequent adoption of the low-energy structure may augment helical bundle formation and perhaps be related to a concomitant loss of immunoreactivity. These results may have implications in the development of HIV-1 fusion inhibitors and vaccines.

Anti-Human Immunodeficiency Virus Type 1 (HIV-1) Antibodies 2F5 and 4E10 Require Surprisingly Few Crucial Residues in the Membrane-Proximal External Region of Glycoprotein gp41 To Neutralize HIV-1

“…However, the functional HIV-1 envelope spike is a putative trimer in which the MPER of one gp41 may be close to the MPER on a neighboring gp41. Moreover, MPER peptides have been shown to self-interact or oligomerize on membranes (1,30,55). We hypothesize that these substitutions weaken a specific interaction between the MPERs of neighboring gp41s.…”

Stable Docking of Neutralizing Human Immunodeficiency Virus Type 1 gp41 Membrane-Proximal External Region Monoclonal Antibodies 2F5 and 4E10 Is Dependent on the Membrane Immersion Depth of Their Epitope Regions

“…Previously, MPER peptide structures in solution have been defined to be random by CD spectroscopic analysis (21). However, more defined secondary structures have been described for some shorter peptides (D 664 -K 683 ) both in solution and in micelle-or liposomebound states in infrared (17,26,30) and CD spectroscopic studies (16). More recently, nuclear magnetic resonance spectroscopic studies of micelle-bound peptides corresponding to E 662 -K 683 (31) and S 649 -K 683 (8) revealed that the C-terminal half of MPER consists of two shorter helices separated by a short hinge and that the N-terminal half of MPER is mostly disordered.…”

Identification of the LWYIK Motif Located in the Human Immunodeficiency Virus Type 1 Transmembrane gp41 Protein as a Distinct Determinant for Viral Infection

“…The dye transfer assay reinforced the notion that the pre-TM region participates in formation and expansion of fusion pores (46). Biophysical studies showed that the abilities of peptides derived from residues 664 to 683 to adopt a helical structure and form homo-oligomers in solution and membranes correlate with their abilities to induce vesicle fusion and inhibit gp41-induced cell-cell fusion (58,64). This sequence is thought to specifically interact with cholesterol-containing membranes, since cholesterol and sphingomyelin in liposomes promote pre-TM peptide surface self-aggregation and destabilization of the membrane architecture (59).…”