Aligned Assembly in a 2-D Gel of a Water-Soluble Peptide

We demonstrate the assembly of a compact, gel-like Langmuir-Blodgett film of rods formed by self-assembly of a β-sheet-forming water-soluble peptide, Ac-IKHLSVN-NH₂, at the surface of aqueous electrolytes. We characterize surface pressure hysteresis and demonstrate shear stiffening of the surface caused by area cycling, which we interpret as due to rearrangement and alignment of the rods. We show strong effects of the electrolyte on the assembly of the elementary rods, which can be related to the Hofmeister series and interpreted by effects on the interaction energies mediated by ions and water. Formation of β-sheet structures and assembly of these into surface-segregated semicrystalline gels was strongly promoted by ammonium sulfate electrolyte. With ammonium sulfate electrolyte as subphase for Langmuir-Blodgett film deposition, shear stiffening by surface area cycling resulted in very compact films on transfer to a substrate.

Transient fibril structures facilitating nonenzymatic self-replication

An emerging new direction of research focuses on developing "self-synthesizing materials", those supramolecular structures that can promote their own formation by accelerating the synthesis of building blocks and/or an entire assembly. It was postulated recently that practical design of such systems can benefit from the ability to control the assembly of amphiphilic molecules into nanostructures. We describe here the self-assembly pathway of short amphiphilic peptides into various forms of soluble β-sheet structures--β-plates, fibrils, and hollow nanotubes--and their consequent activity as autocatalysts for the synthesis of monomeric peptides from simpler building blocks. A detailed kinetic analysis of both the self-assembly and self-replication processes allows us to suggest a full model and simulate the replication process, revealing that only specific structures, primarily fibrils that are stable within the solution for a time shorter than a few hours, can be active as catalysts. Interestingly, we have found that such a process also induces fibril reproduction, in a mechanism very similar to the propagation of prion proteins by transmission of misfolded states.

Syntheses and self-assembling behaviors of pentagonal conjugates of tryptophane zipper-forming peptide

Pentagonal conjugates of tryptophane zipper-forming peptide (CKTWTWTE) with a pentaazacyclopentadecane core (Pentagonal-Gly-Trpzip and Pentagonal-Ala-Trpzip) were synthesized and their self-assembling behaviors were investigated in water. Pentagonal-Gly-Trpzip self-assembled into nanofibers with the width of about 5 nm in neutral water (pH 7) via formation of tryptophane zipper, which irreversibly converted to nanoribbons by heating. In contrast, Pentagonal-Ala-Trpzip formed irregular aggregates in water.

Self-assembly of nanofiber with uniform width from wheel-type trigonal-beta-sheet-forming peptide

A novel C3 symmetric peptide conjugate "Wheel-FKFE" consisting of three beta-sheet-forming peptides with wheel-like arrangement is developed, and the morphology of self-assembled peptide conjugates in aqueous solutions is observed at various pH. The CD spectra of Wheel-FKFE show the formation of beta-sheet structures in pH 6.9 phosphate buffer, whereas random structures are formed in aqueous HCl (pH 3.3) and NaOH (pH 11) solutions. In transmission electron microscopy, nanofibers with a uniform width of 3-4 nm and lengths of several micrometers are observed in pH 6.9 phosphate buffer, whereas nanorods with the width of several nanometers and the length of several tens of nanometers are observed for that of aqueous HCl (pH 3.3) and NaOH (pH 11) solutions. The uniform width (3-4 nm) of the fibers observed in neutral solution indicates formation of columnar self-assembly of Wheel-FKFEs. The fluorescence spectrum of polarity sensitive dye, sodium 8-anilino-1-naphthalenesulfonate (ANS), in the presence of Wheel-FKFE fibers revealed that the polarity inside the fibers corresponds to that of acetone, indicating that the internal space of the fibers possesses medium hydrophobic environment.

Self-assembly of surfactant-like peptides

Inspired by recent work describing surfactant-like peptides, we have carried out a systematic study on peptides with the underlying composition of V6D2, altering the absolute sequence to determine the importance of the surfactant-like structure. All of the peptides examined here formed self-assembled structures in water. However, in contrast to other reports, we have found a surprising diversity of structures including fibers, tapes, and twisted ribbons but an absence of the vesicles and nanotubes described previously. Further investigations demonstrated that peptide purity plays a significant role in the outcome of the self-assembly. Different batches behave very differently, which can be linked to the compositions of these batches. This work shows that there is a need for not only rational design but also ease of synthesis of the building blocks for self-assembled structures.

The structure of nanotubes formed by diphenylalanine, the core recognition motif of Alzheimer's β-amyloid polypeptide

Alzheimer's beta-amyloid diphenylalanine motif has previously been shown to self-assemble into discrete and extraordinary stiff nanotubes; these nanotubes were initially thought to be distinct from the single crystal structure of diphenylalanine, but it is now shown that the X-ray powder diffraction pattern of the nanotubes is identical to the simulated pattern for the single crystal structure, affording a new foundation for understanding and rationalizing the properties of this remarkable organic material.