jp8b08424_si_001.pdf (1.61 MB)
Helical Structure of Recombinant Melittin
journal contribution
posted on 2018-12-20, 00:00 authored by Lisa S. Ramirez, Jayanti Pande, Alexander ShekhtmanMelittin
is an extensively studied, 26-residue toxic peptide from
honey bee venom. Because of its versatility in adopting a variety
of secondary (helix or coil) and quaternary (monomer or tetramer)
structures in various environments, melittin has been the focus of
numerous investigations as a model peptide in protein folding studies
as well as in studies involving binding to proteins, lipids, and polysaccharides.
A significant body of evidence supports the view that melittin binds
to these macromolecules in a predominantly helical conformation, but
detailed structural knowledge of this conformation is lacking. In
this report, we present nuclear magnetic resonance (NMR)-based structural
insights into the helix formation of recombinant melittin in the presence
of trifluoroethanol (TFE): a known secondary structure inducer in
peptides. These studies were performed at neutral pH, with micromolar
amounts of the peptide. Using nuclear Overhauser effect (NOE)-derived
distance restraints from three-dimensional NMR spectra, we determined
the atomic resolution solution NMR structure of recombinant melittin
bearing a TFE-stabilized helix. To circumvent the complications with
structure determination of small peptides with high conformational
flexibility, we developed a workflow for enhancing proton NOEs by
increasing the viscosity of the medium. In the TFE-containing medium,
recombinant monomeric melittin forms a long, continuous helical structure,
which consists of the N- and C-terminal α-helices and the noncanonical
310-helix in the middle. The noncanonical 310-helix is missing in the previously solved X-ray structure of tetrameric
melittin and the NMR structure of melittin in methanol. Melittin’s
structure in TFE-containing medium provides insights into melittin’s
conformational transitions, which are relevant to the peptide’s
interactions with its biological targets.