The role of aromatic residues in controlling the supramolecular chirality of short amphiphilic peptides

Although the relationship between molecular and supramolecular chirality remains elusive,the existing results have demonstrated the vital role of hydrophilic motifs in controlling the supramolecular handedness of peptide nanofibrils compared with hydrophobic ones.However,unlike conventional hydrophobic residues,we speculate that aromatic hydrophobic residues are mostly likely to play a unique role in regulating the supramolecular handedness because theπ–πstacking interactions of their side chains are directional like hydrogen bonding and can direct high levels of self-assembly due to the geometric confining of aromatic rings.To confirm this hypothesis,we here design a series of amphiphilic short peptides,with their hydrophobic motifs being composed of aromatic residues.Their short lengths not only favor their structural stability,synthesis,and sequence variation but also enable us to readily link their molecular and supramolecular structures.Through the combination of experiments and theoretical simulations,we demonstrate that the peptides containing L-form aromatic residues form left-handed nanofibrils while those containing D-form aromatic residues assemble into right-handed ones,irrespective of the chirality of their C-terminal hydrophilic residue.Theoretical calculations revealed that the stacking of aromatic side chains betweenβ-strands directed the twisting direction of theβ-sheets formed,with L-and D-form phenylalanine side chains stacking in a clockwise and anti-clockwise way,and more ordered and stronger aromatic stacking for homochiral peptides facilitated the formation of nanofibrils with a marked tubular feature.This study has bridged the knowledge gap in our understanding of how aromatic residues affect the supramolecular chirality of short peptides.

Engineering and preliminary evaluation of multiple non-equilibrium nanostructures from a single peptide amphiphile

Compared with thermodynamically equilibrium supramolecular assemblies, non-equilibrium assemblies from the same building blocks have attracted increasing attentions because their diverse structures and dynamic natures may impart the assemblies with novel functionalities. However, facile access to non-equilibrium assemblies remains a formidable challenge. Herein, we endeavored to exploit various solvent-anti-solvent methods to achieve it using peptide amphiphile C16-VVAAEE-NH_(2) as a model. Through systematical utilization of dialysis, ultrasonic and stirring-dropping methods, as well as tuning of processing parameters, we demonstrated the successful formation of diverse non-equilibrium nanostructures with distinct morphologies and structures that significantly deviate from the thermodynamically favored twisted long ribbons. Additionally, these metastable nanostructures ultimately underwent spontaneous transformation into thermodynamically stable states. The transformation processes of three representative non-equilibrium assemblies were also demonstrated and characterized in detail using transmission electron microscopy, circular dichroism spectrum, and thioflavin T fluorescence spectrum. Furthermore, non-equilibrium assemblies exhibited various degrees of cytotoxic effects, which may stem from their spontaneous, dynamic transformation and interactions with cellular membranes. This study offers valuable approaches for direct access to diverse non-equilibrium supramolecular nanostructures from self-assembling peptide, and also has implications for the development of advanced materials with unprecedented biological functions.

Sulfated GAG mimetic peptide nanofibers enhance chondrogenic differentiation of mesenchymal stem cells in 3D in vitro models

Articular cartilage,which is exposed to continuous repetitive compressive stress,has limited self-healing capacity in the case of trauma.Thus,it is crucial to develop new treatment options for the effective regeneration of the cartilage tissue.Current cellular therapy treatment options are microfracture and autologous chondrocyte implantation;however,these treatments induce the formation of fibrous cartilage,which degenerates over time,rather than functional hyaline cartilage tissue.Tissue engineering studies using biodegradable scaffolds and autologous cells are vital for developing an effective long-term treatment option.3D scaffolds composed of glycosaminoglycan-like peptide nanofibers are synthetic,bioactive,biocompatible,and biodegradable and trigger cell-cell interactions that enhance chondrogenic differentiation of cells without using any growth factors.We showed differentiation of mesenchymal stem cells into chondrocytes in both 2D and 3D culture,which produce a functional cartilage extracellular matrix,employing bioactive cues integrated into the peptide nanofiber scaffold without adding exogenous growth factors.

Control of secondary structure and morphology of peptide-guanidiniocarbonylpyrrole conjugates by variation of the chain length

Peptide amphiphiles with well-organized secondary structure are an important family of molecules that are known to assemble into a variety of nanostructures.In this work,we present three guanidiniocarbonylpyrrole(GCP)containing peptide amphiphiles,which show versatile morphology and secondary structure changes as a result of different chain lengths and in different concentration regimes.The random coil conformation,α-helix,andβ-sheet are obtained for peptide 1,peptide 2,and peptide 3,respectively under neutral aqueous conditions.Furthermore,all peptide amphiphiles can aggregate to form nanoparticles at low concentrations.However,at high concentrations,peptide 1 selfassembles into left-ha nded twisted helical fibers,while longer bamboo-like mo rphology can be obse rved exclusively for peptide 2.For peptide 3,freshly prepared samples show uniform spherical morphology,whereas an obvious morphological transition from original nanoparticles to disordered fibers was realized after incubating for one week.These fascinating morphology changes were determined by the combination of circular dichroism,dynamic light scattering,transmission electron microscopy,atomic force microscopy,and theoretical calculations.

ROS-initiated in-situ polymerization of diacetylene-containing lipidated peptide amphiphile in living cells

Recently,in-situ polymerization inside living cells has attracted much attention due to the efficient cellular internalization and elevated drug retention.However,the lack of tracking of the in-situ polymerization process and the unclear effects of polymerization on cellular functions restrict its biomedical applications.Herein,we designed a Y-shaped diacetylene-containing lipidated peptide amphiphile(YDLPA1)with positive charges,which underwent in-situ polymerization initiated by reactive oxygen species in the intracellular microenvironment.In comparison,zwitterionic YDLPA2 and negatively charged Y-DLPA3 were polymerized in aqueous solution,but cannot polymerize in the intracellular microenvironment.The polymerized Y-DLPA1 with red fluorescence provides a platform to label cells for long-term tracking studies.This polymerization reaction induced tumor cell apoptosis,increased cell viscosity and decreased cell motility,which potentially inhibited tumor metastasis and served as a novel antitumor agent.This work provides a novel strategy to track in-situ polymerization process and modulate cell biofunctions.