Tuning the Structural Integrity and Mechanical Properties of Globular Protein Vesicles by Blending Crosslinkable and NonCrosslinkable Building Blocks

Engineered Proteins and Materials Utilizing Residue-Specific Noncanonical Amino Acid Incorporation

The incorporation of noncanonical amino acids into proteins and protein-based materials has significantly expanded the repertoire of available protein structures and chemistries. Through residue-specific incorporation, protein properties can be globally modified, resulting in the creation of novel proteins and materials with diverse and tailored characteristics. In this review, we highlight recent advancements in residue-specific incorporation techniques as well as the applications of the engineered proteins and materials. Specifically, we discuss their utility in bio-orthogonal noncanonical amino acid tagging (BONCAT), fluorescent noncanonical amino acid tagging (FUNCAT), threonine-derived noncanonical amino acid tagging (THRONCAT), cross-linking, fluorination, and enzyme engineering. This review underscores the importance of noncanonical amino acid incorporation as a tool for the development of tailored protein properties to meet diverse research and industrial needs.

Genetically Fusing Order-Promoting and Thermoresponsive Building Blocks to Design Hybrid Biomaterials

The unique biophysical and biochemical properties of intrinsically disordered proteins (IDPs) and their recombinant derivatives, intrinsically disordered protein polymers (IDPPs) offer opportunities for producing multistimuli-responsive materials; their sequence-encoded disorder and tendency for phase separation facilitate the development of multifunctional materials. This review highlights the strategies for enhancing the structural diversity of elastin-like polypeptides (ELPs) and resilin-like polypeptides (RLPs), and their self-assembled structures via genetic fusion to ordered motifs such as helical or beta sheet domains. In particular, this review describes approaches that harness the synergistic interplay between order-promoting and thermoresponsive building blocks to design hybrid biomaterials, resulting in well-structured, stimuli-responsive supramolecular materials ordered on the nanoscale.

Rational design and engineering of polypeptide/protein vesicles for advanced biological applications

Synthetic vesicles have gained considerable popularity in recent years for numerous biological and medical applications. Among the various types of synthetic vesicles, the utilization of polypeptides and/or proteins as fundamental constituents has garnered significant interest for vesicle construction owing to the unique bio-functionalities inherent in rationally designed amino acid sequences. Especially the incorporation of functional proteins onto the vesicle surface facilitates a wide range of advanced biological applications that are not easily attainable with traditional building blocks, such as lipids and polymers. The main goal of this review is to provide a comprehensive overview of the latest advancements in polypeptide/protein vesicles. Moreover, this review encompasses the rational design and engineering strategies employed in the creation of polypeptide/protein vesicles, including the synthesis of building blocks, the modulation of their self-assembly, as well as their diverse applications. Furthermore, this work includes an in-depth discussion of the key challenges and opportunities associated with polypeptide/protein vesicles, providing valuable insights for future research. By offering an up-to-date review of this burgeoning field of polypeptide/protein vesicle research, this review will shed light on the potential applications of these biomaterials.

Temperature-responsive membrane permeability of recombinant fusion protein vesicles

In this study, we investigate the changes in the permeability of the recombinant fusion protein vesicles with different membrane structures as a function of solution temperature. The protein vesicles are self-assembled from recombinant fusion protein complexes composed of an mCherry fused with a glutamic acid-rich leucine zipper and a counter arginine-rich leucine zipper fused with an elastin-like polypeptide (ELP). We have found that the molecular weight cut-off (MWCO) of the protein vesicle membranes varies inversely with solution temperature by monitoring the transport of fluorescent-tagged dextran dyes with different molecular weights. The temperature-responsiveness of the protein vesicle membranes is obtained from the lower critical solution temperature behavior of ELP in the protein building blocks. Consequently, the unique vesicle membrane structures with different single-layered and double-layered ELP organizations impact the sensitivity of the permeability responses of the protein vesicles. Single-layered protein vesicles with the ELP domains facing the interior show more drastic permeability changes as a function of temperature than double-layered protein vesicles in which ELP blocks are buried inside the membranes. This work about the temperature-responsive membrane permeability of unique protein vesicles will provide design guidelines for new biomaterials and their applications, such as drug delivery and synthetic protocell development.

Expanding the chemical repertoire of protein-based polymers for drug-delivery applications

Expanding the chemical repertoire of natural and artificial protein-based polymers (PBPs) can enable the production of sequence-defined, yet chemically diverse, biopolymers with customized or new properties that cannot be accessed in PBPs composed of only natural amino acids. Various approaches can enable the expansion of the chemical repertoire of PBPs, including chemical and enzymatic treatments or the incorporation of unnatural amino acids. These techniques are employed to install a wide variety of chemical groups-such as bio-orthogonally reactive, cross-linkable, post-translation modifications, and environmentally responsive groups-which, in turn, can facilitate the design of customized PBP-based drug-delivery systems with modified, fine-tuned, or entirely new properties and functions. Here, we detail the existing and emerging technologies for expanding the chemical repertoire of PBPs and review several chemical groups that either demonstrate or are anticipated to show potential in the design of PBP-based drug delivery systems. Finally, we provide our perspective on the remaining challenges and future directions in this field.

Protein Vesicles with pH-Responsive Disassembly

Protein biomaterials offer several advantages over those made from other components because their amino acid sequence can be precisely controlled with genetic engineering to produce a diverse set of material building blocks. In this work, three different elastin-like polypeptide (ELP) sequences were designed to synthesize pH-responsive protein vesicles. ELPs undergo a thermally induced hydrophobic transition that enables self-assembly of different kinds of protein biomaterials. The transition can be tuned by the composition of the guest residue, X, within the ELP pentapeptide repeat unit, VPGXG. When the guest residue is substituted with an ionizable amino acid, such as histidine, the ELP undergoes a pH-dependent hydrophobic phase transition. We used pH-responsive ELPs with different levels of histidine substitution, in combination with leucine zippers and globular, functional proteins, to fabricate protein vesicles. We demonstrate pH-dependent self-assembly, diameter, and disassembly of the vesicles using a combination of turbidimetry, dynamic light scattering, microscopy, and small angle X-ray scattering. As the ELP transition is dependent on the sequence, the vesicle properties also depend on the histidine content in the ELP building blocks. These results demonstrate the tunability of protein vesicles endowed with pH responsiveness, which expands their potential in drug-delivery applications.

Tuning C-Phycocyanin Photoactivity via pH-Mediated Assembly-Disassembly

Environment-triggered protein conformational changes have garnered wide interest in both fundamental research, for deciphering in vivo acclimatory responses, and practical applications, for designing stimuli-responsive probes. Here, we propose a protein-chromophore regulatory mechanism that allows for manipulation of C-phycocyanin (C-PC) from Spirulina platensis by environmental pH and UV irradiation. Using small-angle X-ray scattering, a pH-mediated C-PC assembly-disassembly pathway, from monomers to nonamers, was unraveled. Such flexible protein matrices impart tunability to the embedded tetrapyrroles, whose photochemical behaviors were found to be modulated by protein assembly states. UV irradiation on C-PC triggers pH-dependent singlet oxygen (¹O₂) generation and conformational changes. Intermolecular photo-crosslinking occurs at pH 5.0 via dityrosine species, which bridges solution-based C-PC oligomers into unprecedented dodecamers and 24-mers. These supramolecular assemblies impart C-PC at pH 5.0, which significantly enhanced ¹O₂ yield, fluorescence, and photostability relative to those at other pH values, a finding that makes C-PC appealing for tumor-targeted photodynamic therapy.

Thermosensitive Vesicles from Chemically Encoded Lipid-Grafted Elastin-like Polypeptides

Biomimetic design to afford smart functional biomaterials with exquisite properties represents synthetic challenges and provides unique perspectives. In this context, elastin-like polypeptides (ELPs) recently became highly attractive building blocks in the development of lipoprotein-based membranes. In addition to the bioengineered post-translational modifications of genetically encoded recombinant ELPs developed so far, we report here a simple and versatile method to design biohybrid brush-like lipid-grafted-ELPs using chemical post-modification reactions. We have explored a combination of methionine alkylation and click chemistry to create a new class of hybrid lipoprotein mimics. Our design allowed the formation of biomimetic vesicles with controlled permeability, correlated to the temperature-responsiveness of ELPs.