Structural and Functional Properties of the Membranotropic HIV-1 Gp41 Loop Region are Modulated by its Intrinsic Hydrophobic Core.

Weizmann Institute of Science, Israel;
Journal of Biological Chemistry (Impact Factor: 4.65). 08/2013; DOI: 10.1074/jbc.M113.496646
Source: PubMed

ABSTRACT The gp41 disulfide loop region switches from a soluble state to a membrane-bound state during the human immunodeficiency virus type 1 (HIV-1) envelope (ENV)-mediated membrane fusion process. The loop possesses a hydrophobic core at the center of the region with an unusual basic residue (Lys 601). Furthermore, two loop core mutations, K601A and L602A, are found to inhibit HIV-1 infectivity while keeping wild type-like levels of the ENV, implying that they exert an inhibitory effect on gp41 during the membrane fusion event. Here, we investigated the mode of action of these mutations on the loop region. We show that the K601A mutation but not the L602A, abolished the binding of a loop-specific monoclonal antibody to a loop domain peptide. Additionally, the K601A, but not the L602A, impaired disulfide bond formation in the peptides. This was correlated with changes in the circular dichroism spectrum imposed by the K601A mutation. In the membrane, however, the L602A, but not the K601A, reduced the lipid mixing ability of the loop peptides, which was correlated with decreased alpha-helical content of the L602A mutant. The results suggest that the Lys601 residue provides a moderate hydrophobicity level within the gp41 loop core that contributes to the proper structure and function of the loop inside and outside the membrane. Since basic residues are found between the loop Cys residues of several lentiviral fusion proteins; the findings may contribute to understanding the fusion mechanism of other viruses as well.

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May 28, 2014