Solid-State NMR Evidence for β-Hairpin Structure within MAX8 Designer Peptide Nanofibers

MAX8, a designer peptide known to undergo self-assembly following changes in temperature, pH, and ionic strength, has demonstrated usefulness for tissue engineering and drug delivery. It is hypothesized that the self-assembled MAX8 nanofiber structure consists of closed beta-hairpins aligned into antiparallel beta-sheets. Here, we report evidence from solid-state NMR spectroscopy that supports the presence of the hypothesized beta-hairpin conformation within the nanofiber structure. Specifically, our C-13-C-13 two-dimensional exchange data indicate spatial proximity between V3 and K17, and C-13-C-13 dipolar coupling measurements reveal proximity between the V3 and V18 backbone carbonyls. Moreover, isotopic dilution of labeled MAX8 nanofibers did not result in a loss of the C-13-C-13 dipolar couplings, showing that these couplings are primarily intramolecular. NMR spectra also indicate the existence of a minor conformation, which is discussed in terms of previously hypothesized nanofiber physical cross-linking and possible nanofiber polymorphism.