Instructed Assembly of Peptides for Intracellular Enzyme Sequestration

Assemblies of Peptides in a Complex Environment and their Applications

Using peptide assemblies with emergent properties to achieve elaborate functions has attracted increasing attention in recent years. Besides tailoring the self-assembly of peptides in vitro, peptide research is advancing into a new and exciting frontier: the rational design of peptide assemblies (or their derivatives) for biological functions in a complex environment. This Minireview highlights recent developments in peptide assemblies and their applications in biological systems. After introducing the unique merits of peptide assemblies, we discuss the recent progress in designing peptides (or peptide derivatives) for self-assembly with conformational control. Then, we describe biological functions of peptide assemblies, with an emphasis on approach-instructed assembly for spatiotemporal control of peptide assemblies, in the cellular context. Finally, we discuss the future promises and challenges of this exciting area of chemistry.

Activatable NIR Fluorescence/MRI Bimodal Probes for in Vivo Imaging by Enzyme-Mediated Fluorogenic Reaction and Self-Assembly

Stimuli-responsive in situ self-assembly of small molecules to form nanostructures in living subjects has produced promising tools for molecular imaging and tissue engineering. However, controlling the self-assembly process to simultaneously activate multimodality imaging signals in a small-molecule probe is challenging. In this paper, we rationally integrate a fluorogenic reaction into enzyme-responsive in situ self-assembly to design small-molecule-based activatable near-infrared (NIR) fluorescence and magnetic resonance (MR) bimodal probes for molecular imaging. Using alkaline phosphatase (ALP) as a model target, we demonstrate that probe (P-CyFF-Gd) can be activated by endogenous ALP overexpressed on cell membranes, producing membrane-localized assembled nanoparticles (NPs) that can be directly visualized by cryo-SEM. Simultaneous enhancements in NIR fluorescence (>70-fold at 710 nm) and r₁ relaxivity (∼2.3-fold) enable real-time, high-sensitivity, high-spatial-resolution imaging and localization of the ALP activity in live tumor cells and mice. P-CyFF-Gd can also delineate orthotopic liver tumor foci, facilitating efficient real-time, image-guided surgical resection of tumor tissues in intraoperative mice. This strategy combines activatable NIR fluorescence via a fluorogenic reaction and activatable MRI via in situ self-assembly to promote ALP activity imaging, which could be applicable to design other activatable bimodal probes for in vivo imaging of enzyme activity and locations in real time.

Supramolecular Assemblies of Peptides or Nucleopeptides for Gene Delivery

Using non-covalent interactions between nucleic acids (DNA, siRNA, miRNA, and mRNA) with peptides or nucleopeptides is a promising strategy to construct supramolecular assemblies for gene delivery and therapy. Comparing to conventional strategies for gene delivery, the assemblies of peptides or nucleopeptides provide several unique advantages: i) reversible interactions between the assemblies and the nucleic acids; ii) minimal immunogenicity; iii) biocompatibility. This field has advanced considerably in recent years so that it is worth summarizing the recent progresses and future challenges. In this review, we introduce the development of assemblies of peptides or nucleopeptides for applications in gene delivery and related fields. After introducing the promises of gene therapy and the current strategies for the delivery, we discuss the unique advantage of using peptide assemblies for gene delivery. Then we describe several representative strategies for gene delivery by the assemblies of peptides or nucleopeptides. Finally, we discuss the key factors for designing such assemblies for gene delivery, and speculate future directions and challenges in the field, particularly the rational design and the spatiotemporally controlled release in live cells.

Intercellular Instructed-Assembly Mimics Protein Dynamics To Induce Cell Spheroids

Cell-mediated remodeling of extracellular matrix (ECM) plays important roles for cell functions, but it is challenging to develop synthetic materials for mimicking such a dynamic aspect of proteins in ECM. Here we show that intercellular morphological transition of peptide assemblies mimic the unfolding of fibronectin, thus enabling formation of spheroids from a monolayer of cells. Specifically, the phosphopeptide self-assembles to form nanoparticles, which turns into nanofibers upon partial dephosphorylation catalyzed by enzymes (e.g., phosphatases) at intercellular space. Occurring between HS-5 cells, such an enzyme-instructed self-assembly enables a sheet of the HS-5 cells to form cell spheroids. Structure-activity investigation reveals that proteolytic stability, dephosphorylation, and biotin conjugation of the peptides are indispensable for forming the cell spheroids. Further mechanism study indicates that the intercellular assemblies interact with multiple ECM components (e.g., laminin, collagens III and IV) to drive the formation of the cell spheroids. As the first example of intercellular instructed-assembly from homotypic precursors, this work illustrates a new approach that uses cell-responsive peptide assemblies to mimic protein dynamics for control cell behaviors.

Iron gall ink revisited: hierarchical formation of Fe(iii)–tannic acid coacervate particles in microdroplets for protein condensation

We report a hierarchical self-assembly approach to form Fe(iii)–tannic acid particles in microdroplets and its application to protein condensation.