MagicWand: A Single, Designed Peptide That Assembles to Stable, Ordered α-Helical Fibers

Abstract

We describe a straightforward single-peptide design that self-assembles into extended and thickened nano-to-mesoscale fibers of remarkable stability and order. The basic chassis of the design is the well-understood dimeric alpha-helical coiled-coil motif. As such, the peptide has a heptad sequence repeat, abcdefg , with isoleucine and leucine residues at the a and d sites to ensure dimerization. In addition, to direct staggered assembly of peptides and to foster fibrillogenesisthat is, as opposed to blunt-ended discrete speciesthe terminal quarters of the peptide are cationic and the central half anionic with lysine and glutamate, respectively, at core-flanking e and g positions. This +,-,-,+ arrangement gives the peptide its name, MagicWand (MW). As judged by circular dichroism (CD) spectra, MW assembles to alpha-helical structures in the sub-micromolar range and above. The thermal unfolding of MW is reversible with a melting temperature >70 degrees C at 100 muM peptide concentration. Negative-stain transmission electron microscopy (TEM) of MW assemblies reveals stiff, straight, fibrous rods that extended for tens of microns. Moreover, different stains highlight considerable order both perpendicular and parallel to the fiber long axis. The dimensions of these features are consistent with bundles of long, straight coiled alpha-helical coiled coils with their axes aligned parallel to the long axis of the fibers. The fiber thickening indicates inter-coiled-coil interactions. Mutagenesis of the outer surface of the peptide i.e., at the b and f positionscombined with stability and microscopy measurements, highlights the role of electrostatic and cation-pi interactions in driving fiber formation, stability and thickening. These findings are discussed in the context of the growing number of self-assembling peptide-based fibrous systems.

The non-covalent decoration of self-assembling protein fibers

“…Both systems have an overall charge of þ1 per building block (a heterodimer in the case of 3rd-generation SAFs, and a monomer for MW1) and clear, persistent ultrastructure indicative of high levels of order. However, the sequence features of the designs, and how these may present in the ultrastructure and order are very different: both the 2nd and the 3rd-generation SAFs have a cluster of positive charge on the outer surfaces of the coiled-coil [22], whereas the MW1 has a single positive charge [26]. Interestingly, the biotineDE 3 tag recruited to the 3rd-generation SAFs, but not to MW1 fibers, Fig.…”

“…Specific binding of the tags for the SAFs is clearly an important criterion; hence any binding of the biotineDE 3 tag, the best binder of the SAFs studied above, was tested against 3rd-generation SAFs and MagicWand (MW1) [21,26]. Both systems have an overall charge of þ1 per building block (a heterodimer in the case of 3rd-generation SAFs, and a monomer for MW1) and clear, persistent ultrastructure indicative of high levels of order.…”

“…1. In addition, we have described a 3rd-generation SAF design [21], and also a single-peptide a-helical fiber-forming system, MagicWand [26], which serve as useful controls in the studies reported here.…”

Peptide Self-Assembled Nanostructures for Drug Delivery Applications

“…The hydrophobic residues could promote the helix oligomerization through hydrophobic collapse. Another nanofibrous structure could also be formed using the peptides with central Glu amino acid and Lys amino acid at the end of the sequence through ionic interactions [91].…”

Bioproduction and self-assembly of designer peptides

“…165 Due to the destabilising placement of polar residues in the coiled-coil core, peptide fibrils were thermally unstable and required low temperatures for assembly. 165,167 Assembled morphology was controlled by the addition of modified peptides designed to introduce kinks 168 and branches 169 into the fibrils. More recent work by the same group has given the peptides hSAF AAA -p1 and hSAF AAA -p2.…”