Artificial Intracellular Filaments

Directly observing intracellular nanoparticle formation with nanocomputed tomography

Directly observing intracellular nanostructure formation remains challenging. In this work, using a rationally designed small-molecule 4-nitrobenzyl carbamate-Cys(SEt)-Asp-Asp-Phe(iodine)-2-cyano-benzothiazole (NBC-Iod-CBT), we directly observed intracellular nanoparticle formation with nanocomputed tomography (nano-CT). In vitro, upon glutathione reduction and nitroreductase (NTR) cleavage, NBC-Iod-CBT undergoes a CBT-Cys click condensation reaction to self-assemble nanoparticles Iod-CBT-NPs with an average linear absorption coefficient (LAC) value of 0.182 ± 0.078 μm^-1 to x-ray. Nano-CT imaging of the NBC-Iod-CBT-treated, NTR-overexpressing HeLa cells showed the existence of Iod-CBT-NPs in their cytoplasm with an average LAC value of 0.172 ± 0.032 μm^-1 We anticipate that our strategy could help people to deeply understand the formation mechanism of intracellular nanostructures in the near future.

Enzymatic Noncovalent Synthesis

Enzymatic reactions and noncovalent (i.e., supramolecular) interactions are two fundamental nongenetic attributes of life. Enzymatic noncovalent synthesis (ENS) refers to a process where enzymatic reactions control intermolecular noncovalent interactions for spatial organization of higher-order molecular assemblies that exhibit emergent properties and functions. Like enzymatic covalent synthesis (ECS), in which an enzyme catalyzes the formation of covalent bonds to generate individual molecules, ENS is a unifying theme for understanding the functions, morphologies, and locations of molecular ensembles in cellular environments. This review intends to provide a summary of the works of ENS within the past decade and emphasize ENS for functions. After comparing ECS and ENS, we describe a few representative examples where nature uses ENS, as a rule of life, to create the ensembles of biomacromolecules for emergent properties/functions in a myriad of cellular processes. Then, we focus on ENS of man-made (synthetic) molecules in cell-free conditions, classified by the types of enzymes. After that, we introduce the exploration of ENS of man-made molecules in the context of cells by discussing intercellular, peri/intracellular, and subcellular ENS for cell morphogenesis, molecular imaging, cancer therapy, and other applications. Finally, we provide a perspective on the promises of ENS for developing molecular assemblies/processes for functions. This review aims to be an updated introduction for researchers who are interested in exploring noncovalent synthesis for developing molecular science and technologies to address societal needs.

Enzyme-instructed self-assembly of the stereoisomers of pentapeptides to form biocompatible supramolecular hydrogels

This article reports enzyme-instructed self-assembly (EISA) of stereoisomers of pentapeptides as a simple approach for generating biocompatible supramolecular hydrogels as potential soft bionanomaterials. Peptide-based supramolecular hydrogels are emerging as a new type of biomaterials. The use of tyrosine phosphate offers a trigger for enzymatic hydrogelation, and the incorporation of D-amino acids can increase the proteolytic stability of peptides. This work compared four phosphorpeptides that are stereoisomers in terms of rate of dephosphorylation, proteolytic stability, and cell compatibility. The results show that the naphthyl (Nap)-capped pentapeptides, containing the amino acid sequence of Phe-Phe-Gly-Glu-pTyr, are able to undergo EISA to form the hydrogels consisting the nanofibres of the dephosphorylated pentapeptides. The naphthyl-capped D-phosphopentpeptides, contrasting to a naphthyl-capped D-phosphotripeptide (Nap-D-Phe-D-Phe-D-pTyr), are largely cell compatible. This result, suggesting that the sequence of phophopeptides also dedicates the cell compatibility of the peptide assemblies resulted from EISA, provides useful insights for developing supramolecular hydrogels as potential biomaterials with tailored properties.