De Novo Designed Peptide and Protein Hairpins Self-assemble into Sheets and Nanoparticles

The design and assembly of peptide based materials has advanced considerably, leading to a variety of fibrous, sheet and nanoparticle structures. A remaining challenge is to account for and control different possible supramolecular outcomes accessible to the same or similar peptide building blocks. Here we present a de novo peptide system that forms nanoparticles or sheets depending on the strategic placement of a ‘disulfide pin’ between two elements of secondary structure that drive self-assembly. Specifically, we join homodimerizing and homotrimerizing de novo coiled-coil α-helices with a flexible linker to generate a series of linear peptides. The helices are pinned back-to-back, constraining them as hairpins by a disulfide bond placed either proximal or distal to the linker. Computational modeling and advanced microscopy show that the proximally pinned hairpins self-assemble into nanoparticles, whereas the distally pinned constructs form sheets. These peptides can be made synthetically or recombinantly to allow both chemical modifications and the introduction of whole protein cargoes as required. ### Competing Interest Statement The authors have declared no competing interest. * AFM : atomic force microscopy, CC-Di : homodimeric coiled coil, CC- Tri3 : heterodimeric coiled coil from basis set sequences,[1][1] cfl : 6-carboxyfluorescein, CLEM : correlative light and electron microscopy, cryo- TEM : cryogenic transmission electron microscopy, dist : distal to the hairpin loop, DNA : deoxyribonucleic acid, E. coli : Escherichia coli , FFT : fast Fourier transform, FRET : Förster resonance energy transfer, HEPES : 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer, HP : hairpin, pep : peptide, prot : protein, prox : proximal to the hairpin loop, SAGE : self-assembled peptide cage, SDS-PAGE : sodium dodecylsulfide polyacrylamide gel electrophoresis, sfGFP : super-folder green fluorescent protein, tmr : TAMRA 5(6)-carboxytetramethylrhodamine, TEM : transmission electron microscopy, UA : uranyl acetate. [1]: #ref-1