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Controlled-release materials are desirable for many delivery applications and have been used to improve the efficiency of fertilizers and pesticides in crop management. Due to their potential to reduce application of toxic chemicals while prolonging exposure to active agents, controlled-release nanomaterials are currently being investigated for increasing agricultural production and preventing overfertilization. Hydrogels are underexplored as controlled-release nanomaterials and can deliver many types of cargo, from metal ions to small molecules. Alginate-based hydrogels are biocompatible and their internal carboxylic acids coordinate agriculturally valuable micronutrients like Cu2+, Zn2+, and Ca2+. Hydrogels comprising ionic and nonionic polymers can coordinate agriculturally valuable micronutrients, and the combination of ionic and nonionic polymers results in hydrogels with tunable release profiles. Alginate, for example, contains carboxylates that ionically cross-link with divalent cations like Cu2+, Zn2+, and Ca2+, while polar moieties on chitin enable nonionic coordination. To our knowledge, soft-material copper-loaded nanoparticles have not yet been applied as controlled-release materials for foliar delivery. In this work, we present the synthesis and micronutrient release characteristics of hydrogel nanoparticles containing Cu2+, which is coordinated by ionic and nonionic polymers. Hydrogel nanoparticles (HNPs) were prepared by liquid–liquid emulsion techniques and cross-linked with Cu2+ to form double-network hydrogels made from alginate and non-cross-linking chitin. Nanoparticles (100–300 nm in diameter) were characterized by cryogenic electron microscopy, nanoparticle tracking analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The copper release profiles of HNPs with different polymer compositions were compared. HNPs containing both chitin and alginate released 8–20 times more copper than HNPs with alginate alone, suggesting that the presence of non-cross-linking polymers improves copper release. Thus, HNP delivery characteristics can be tuned by manipulating intraparticle bond dynamics in the hydrogel polymer matrix. 

Nanomaterials acquire a biomolecular corona upon introduction to biological media, leading to biological transformations such as changes in protein function, unmasking of epitopes, and protein fibrilization. Ex vivo studies to investigate the effect of nanoparticles on protein–protein interactions are typically performed in buffer and are rarely measured quantitatively in live cells. Here, we measure the differential effect of silica nanoparticles on protein association in vitro vs. in mammalian cells. BtubA and BtubB are a pair of bacterial tubulin proteins identified inProsthecobacterstrains that self-assemble like eukaryotic tubulin, first into dimers and then into microtubules in vitro or in vivo. Förster resonance energy transfer labeling of each of the Btub monomers with a donor (mEGFP) and acceptor (mRuby3) fluorescent protein provides a quantitative tool to measure their binding interactions in the presence of unfunctionalized silica nanoparticles in buffer and in cells using fluorescence spectroscopy and microscopy. We show that silica nanoparticles enhance BtubAB dimerization in buffer due to protein corona formation. However, these nanoparticles have little effect on bacterial tubulin self-assembly in the complex mammalian cellular environment. Thus, the effect of nanomaterials on protein–protein interactions may not be readily translated from the test tube to the cell in the absence of particle surface functionalization that can enable targeted protein–nanoparticle interactions to withstand competitive binding in the nanoparticle corona from other biomolecules. 

Engineered gold nanoparticles (AuNPs) have great potential in many applications due to their tunable optical properties, facile synthesis, and surface functionalization via thiol chemistry. When exposed to a biological environment, NPs are coated with a protein corona that can alter the NPs’ biological identity but can also affect the proteins’ structures and functions. Protein disulfide isomerase (PDI) is an abundant protein responsible for the disulfide formation and isomerization that contribute to overall cell redox homeostasis and signaling. Given that AuNPs are widely employed in nanomedicine and PDI plays a functional role in various diseases, the interactions between oxidized (oPDI) and reduced (rPDI) with 50 nm citrate-coated AuNPs (AuNPs) are examined in this study using various techniques. Upon incubation, PDI adsorbs to the AuNP surface, which leads to a reduction in its enzymatic activity despite limited changes in secondary structures. Partial enzymatic digestion followed by mass spectrometry analysis shows that orientation of PDI on the NP surface is dependent on both its oxidation state and the PDI:AuNP incubation ratios. 

Studies of proteins from one organism in another organism’s cells have shown that such exogenous proteins stick more, pointing toward coevolution of the cytoplasm and protein surface to minimize stickiness. Here we flip this question around by asking whether exogenous proteins can assemble efficiently into their target complexes in a non-native cytoplasm. We use as our model system the assembly of BtubA and BtubB from Prosthecobacter hosted in human U-2 OS cells. BtubA and B evolved from eukaryotic tubulins after horizontal gene transfer, but they have low surface sequence identity with the homologous human tubulins and do not respond to tubulin drugs such as nocodazole. In U-2 OS cells, BtubA and B assemble efficiently into dimers compared to in vitro, and the wild-type BtubA and B proteins subsequently are able to form microtubules as well. We find that generic crowding effects (Ficoll 70 in vitro) contribute significantly to efficient dimer assembly when compared to sticking interactions (U-2 OS cell lysate in vitro), consistent with the notion that a generic mechanism such as crowding can be effective at driving assembly of exogenous proteins, even when protein-cytoplasm quinary structure and sticking have been modified in a non-native cytoplasm. A simple Monte Carlo model of in vitro and in-cell interactions, treating BtubA and B as sticky dipoles in a matrix of sticky or nonsticky crowders, rationalizes all the experimental trends with two adjustable parameters and reveals nucleation as the likely mechanism for the time-scale separation between dimer- and tubule formation in-cell and in vitro.