Abstract
Most natural biomolecules may exist in either of two enantiomeric forms. Although in nature, amino acid biopolymers are characterized by l-type homochirality, incorporation of d-amino acids in the design of self-assembling peptide motifs has been shown to significantly alter enzyme stability, conformation, self-assembly behavior, cytotoxicity, and even therapeutic activity. However, while functional metabolite assemblies are ubiquitous throughout nature and play numerous important roles including physiological, structural, or catalytic functions, the effect of chirality on the self-assembly nature and function of single amino acids is not yet explored. Herein, we investigated the self-assembly mechanism of amyloid-like structure formation by two aromatic amino acids, phenylalanine (Phe) and tryptophan (Trp), both previously found as extremely important for the nucleation and self-assembly of aggregation-prone peptide regions into functional structures. Employing d-enantiomers, we demonstrate the critical role that amino acid chirality plays in their self-assembly process. The kinetics and morphology of pure enantiomers is completely altered upon their coassembly, allowing to fabricate different nanostructures that are mechanically more robust. Using diverse experimental techniques, we reveal the different molecular arrangement and self-assembly mechanism of the dl-racemic mixtures that resulted in the formation of advanced supramolecular materials. This study provides a simple yet sophisticated engineering model for the fabrication of attractive materials with bionanotechnological applications.
Highlights
Most natural biomolecules may exist in either of two enantiomeric forms
Aromatic amino acids play a crucial role in the formation of functional structures by the self-assembly of proteins and peptides, the major components of life
Our investigation of aromatic amino acid self-assembly together with the demonstration of the involvement of various interactions, such as electrostatic interactions, aromatic π−π stacking, hydrogen bonding, etc., to drive the aggregation process provides the basis for understanding their self-assembly mechanism
Summary
Most natural biomolecules may exist in either of two enantiomeric forms. in nature, amino acid biopolymers are characterized by L-type homochirality, incorporation of D-amino acids in the design of self-assembling peptide motifs has been shown to significantly alter enzyme stability, conformation, self-assembly behavior, cytotoxicity, and even therapeutic activity. Self-assembly into distinct structure is considered to be a promising approach to achieve revolutionary advances in the design and fabrication of attractive functional materials.[1,3] Similar to protein amyloids, self-assembly of amyloid fiber forming single amino acids has been explored to design exciting biomaterials.[4−6] Aromatic amino acids such as Phe, Trp, Tyr, and His are reported to form a wide range of nanostructures including fibers, nanotubes, nanoribbons, twisted nanosheets, dendritic structures, etc., depending on the self-assembly conditions.[5,6] Apart from morphological diversity, a recent report showed the efficiently dense packing of β-Gly crystals along certain crystallographic planes provided a high piezoelectric voltage constant, higher than the voltage produced by any currently used ceramic and polymeric materials.[7] Nonpolar centrosymmetric crystals of α-Gly have been demonstrated to exhibit surface pyroelectricity.[8,9] Recently, our group has revealed the intrinsic fluorescence properties of amyloid-like structures fabricated by single amino acids.[10] The formation, dynamics, and cellular distribution of supramolecular chromophores were detected without the use of an external dye. DL-Phe shown in black, red, and blue, respectively. (j) Mass spectra of the noncovalent assemblies of the intermolecular complexes
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