A novel family of 2Fe-2S proteins, the NEET family, was discovered during the last decade in numerous organisms, including archea, bacteria, algae, plant and human; suggesting an evolutionary-conserved function, potentially mediated by their CDGSH Iron-Sulfur Domain. In human, three NEET members encoded by the CISD1-3 genes were identified. The structures of CISD1 (mitoNEET, mNT), CISD2 (NAF-1), and the plant At-NEET uncovered a homodimer with a unique "NEET fold", as well as two distinct domains: a beta-cap and a 2Fe-2S cluster-binding domain. The 2Fe-2S clusters of NEET proteins were found to be coordinated by a novel 3Cys:1His structure that is relatively labile compared to other 2Fe-2S proteins and is the reason of the NEETs' clusters could be transferred to apo-acceptor protein(s) or mitochondria. Positioned at the protein surface, the NEET's 2Fe-2S's coordinating His is exposed to protonation upon changes in its environment, potentially suggesting a sensing function for this residue. Studies in different model systems demonstrated a role for NAF-1 and mNT in the regulation of cellular iron, calcium and ROS homeostasis, and uncovered a key role for NEET proteins in critical processes, such as cancer cell proliferation and tumor growth, lipid and glucose homeostasis in obesity and diabetes, control of autophagy, longevity in mice, and senescence in plants. Abnormal regulation of NEET proteins was consequently found to result in multiple health conditions, and aberrant splicing of NAF-1 was found to be a causative of the neurological genetic disorder Wolfram Syndrome 2. Here we review the discovery of NEET proteins, their structural, biochemical and biophysical characterization, and their most recent structure-function analyses. We additionally highlight future avenues of research focused on NEET proteins and propose an essential role for NEETs in health and disease. This article is part of a Special Issue entitled: Fe/S proteins: Analysis, structure, function, biogenesis and diseases.

The synthesis of doxorubicin‐loaded metal–organic framework nanoparticles (NMOFs) coated with a stimuli‐responsive nucleic acid‐based polyacrylamide hydrogel is described. The formation of the hydrogel is stimulated by the crosslinking of two polyacrylamide chains, PA and PB, that are functionalized with two nucleic acid hairpins (4) and (5) using the strand‐induced hybridization chain reaction. The resulting duplex‐bridged polyacrylamide hydrogel includes the anti‐ATP (adenosine triphosphate) aptamer sequence in a caged configuration. The drug encapsulated in the NMOFs is locked by the hydrogel coating. In the presence of ATP that is overexpressed in cancer cells, the hydrogel coating is degraded via the formation of the ATP–aptamer complex, resulting in the release of doxorubicin drug. In addition to the introduction of a general means to synthesize drug‐loaded stimuli‐responsive nucleic acid‐based polyacrylamide hydrogel‐coated NMOFs hybrids, the functionalized NMOFs resolve significant limitations associated with the recently reported nucleic acid‐gated drug‐loaded NMOFs. The study reveals substantially higher loading of the drug in the hydrogel‐coated NMOFs as compared to the nucleic acid‐gated NMOFs and overcomes the nonspecific leakage of the drug observed with the nucleic‐acid‐protected NMOFs. The doxorubicin‐loaded, ATP‐responsive, hydrogel‐coated NMOFs reveal selective and effective cytotoxicity toward MDA‐MB‐231 breast cancer cells, as compared to normal MCF‐10A epithelial breast cells.

Because the function of NEET proteins depends on the lability of their clusters, drugs that target the 2Fe2S clusters of NEET proteins could be used as promising anticancer drugs. Antioxid. Redox Signal. 00, 000-000.

A method to assemble light-responsive or pH-responsive microcapsules loaded with different loads (tetramethylrhodamine-modified dextran, TMR-D; microperoxidase-11, MP-11; CdSe/ZnS quantum dots; or doxorubicin-modified dextran, DOX-D) is described. The method is based on the layer-by-layer deposition of sequence-specific nucleic acids on poly(allylamine hydrochloride)-functionalized CaCO3 core microparticles, loaded with the different loads, that after the dissolution of the core particles with EDTA yields the stimuli-responsive microcapsules that include the respective loads. The light-responsive microcapsules are composed of photocleavable o-nitrobenzyl-phosphate-modified DNA shells, and the pH-responsive microcapsules are made of a cytosine-rich layer cross-linked by nucleic acid bridges. Irradiating the o-nitrobenzyl phosphate-functionalized microcapsules, λ = 365 nm, or subjecting the pH-responsive microcapsules to pH = 5.0, results in the cleavage of the microcapsule shells and the release of the loads. Preliminary studies address the cytotoxicity of the DOX-D-loaded microcapsules toward MDA-MB-231 breast cancer cells and normal MCF-10A breast epithelial cells. Selective cytotoxicity of the DOX-D-loaded microcapsules toward cancer cells is demonstrated.

Drug-loaded DNA-capped metal–organic framework nanoparticles are unlocked by pH or Mg2+ ions/ATP triggers, resulting in the release of the loads.

Zeolitic Zn-imidazolate cross-linked framework nanoparticles, ZIF-8 NMOFs, are used as "smart" glucose-responsive carriers for the controlled release of drugs. The ZIF-8 NMOFs are loaded with the respective drug and glucose oxidase (GOx), and the GOx-mediated aerobic oxidation of glucose yields gluconic acid and HO. The acidification of the NMOFs' microenvironment leads to the degradation of the nanoparticles and the release of the loaded drugs. In one sense-and-treat system, GOx and insulin are loaded in the NMOFs. In the presence of glucose, the nanoparticles are unlocked, resulting in the release of insulin. The release of insulin is controlled by the concentration of glucose. In the second sense-and-treat system, the NMOFs are loaded with the antivascular endothelial growth factor aptamer (VEGF aptamer) and GOx. In the presence of glucose, the ZIF-8 NMOFs are degraded, leading to the release of the VEGF aptamer, which acts as a potential inhibitor of the angiogenetic regeneration of blood vessels by VEGF. As calcination of the VEGF-generated blood vessels leads to blindness of diabetic patients, the functional NMOFs might act as "smart" materials for the treatment of macular diseases. The potential cytotoxicity of the NMOFs originated from the GOx-generated HO is resolved by the co-immobilization of the HO-scavanger catalase in the NMOFs.

Nanoparticles consisting of metal-organic frameworks (NMOFs) modified with nucleic acid binding strands are synthesized. The NMOFs are loaded with a fluorescent agent or with the anticancer drug doxorubicin, and the loaded NMOFs are capped by hybridization with a complementary nucleic acid that includes the ATP-aptamer or the ATP-AS1411 hybrid aptamer in caged configurations. The NMOFs are unlocked in the presence of ATP via the formation of ATP-aptamer complexes, resulting in the release of the loads. As ATP is overexpressed in cancer cells, and since the AS1411 aptamer recognizes the nucleolin receptor sites on the cancer cell membrane, the doxorubicin-loaded NMOFs provide functional carriers for targeting and treatment of cancer cells. Preliminary cell experiments reveal impressive selective permeation of the NMOFs into MDA-MB-231 breast cancer cells as compared to MCF-10A normal epithelial breast cells. High cytotoxic efficacy and targeted drug release are observed with the ATP-AS1411-functionalized doxorubicin-loaded NMOFs. The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201702102.conductivity material for fuel cells, [16][17][18] and as a composite material for sensing applications. [4,[19][20][21] Substantial recent efforts are directed toward the development of stimulitriggered reconfigurable nucleic acid structures (DNA switches and DNA machines). [22][23][24][25][26][27] Porous inorganic materials, e.g., SiO 2 nanoparticles, [28] microcapsules, [29] or organic hydrogels, [30][31][32] were loaded with substrates (or drugs) and caged with stimuli-responsive nucleic acid locks. In the presence of appropriate triggers, the stimuli-responsive loaded matrices were unlocked, resulting in the release of the loads. Different stimuli such as pH, [33] light, [34] heat, [35] catalytic nucleic acids, [36] or aptamer-ligand complexes [37] were used to unlock the substrate-loaded materials. Naturally, the capping of the highly porous substrate-loaded MOFs with stimuli-responsive DNAs could yield efficient DNA/ MOFs hybrids as drug delivery systems. Despite the chemical modification of MOFs with stimuli-responsive chemical capping units, [38][39][40][41][42][43] the integration of nucleic acids with MOFs is scarce and involved only the carrying of DNA. [44][45][46][47] Recently, we reported [48] on the successful entrapment of substrates in macrocrystalline MOFs protected by pH-responsive or K + -stabilized G-quadruplex capping units and the triggered unlocking of the MOFs, and the release of loads, by altering the pH, or their treatment with 18-crown-6 ether. While this study demonstrated the successful synthesis of stimuli-responsive DNAgated, substrate-loaded, microcrystalline MOFs, these materials suffer from a basic limitation because they are nonpermeable into cells. That is, their potential application as stimuli-responsive drug carriers is limited. The synthesis of nanometersized MOF particles is well established, [49][50][51][52][53][54] but ...

A generic method of preparing stimuli-responsive substrate-loaded hydrogel microcapsules, composed of polyacrylamide chains cross-linked by nucleic acids, has been described. The triggered release of loads from the microcapsules proceeds via either the formation of an ATP aptamer or a cocaine aptamer, or the pH-induced generation of i-motif structures.