The membrane proximal external region (MPER) of gp41 abuts the viral membrane at the base of HIV-1 envelope
glycoprotein spikes. The MPER is highly conserved and is rich in Trp and other lipophilic residues. The MPER is also required for the
infection of host cells by HIV-1 and is the target of the
broadly neutralizing antibodies, 4E10, 2F5, and Z13e1. These
neutralizing antibodies are valuable tools for understanding relevant conformations of the MPER and for studying HIV-1 neutralization, but multiple approaches used to elicit MPER binding
antibodies with similar neutralization properties have failed. Here we report our efforts to mimic the MPER using linear as well as constrained
peptides. Unnatural
amino acids were also introduced into the core
epitope of 4E10 to probe requirements of antibody binding.
Peptide analogs with C-terminal Api or Aib residues designed to be helical transmembrane (TM) domain surrogates exhibit enhanced binding to the 4E10 and Z13e1
antibodies. However, we find that placement of constrained
amino acids at nonbinding sites within the core
epitope significantly reduce binding. These results are relevant to an understanding of native MPER structure on HIV-1, and form a basis for a chemical synthesis approach to mimic MPER
stricture and to construct an MPER-based
vaccine.