The C-Terminus of the PSMA3 Proteasome Subunit Preferentially Traps Intrinsically Disordered Proteins for Degradation.

The degradation of intrinsically disordered proteins (IDPs) by a non-26S proteasome process does not require proteasomal targeting by polyubiquitin. However, whether and how IDPs are recognized by the non-26S proteasome, including the 20S complex, remains unknown. Analyses of protein interactome datasets revealed that the 20S proteasome subunit, PSMA3, preferentially interacts with many IDPs. In vivo and cell-free experiments revealed that the C-terminus of PSMA3, a 69-amino-acids-long fragment, is an IDP trapper. A recombinant trapper is sufficient to interact with many IDPs, and blocks IDP degradation in vitro by the 20S proteasome, possibly by competing with the native trapper. In addition, over a third of the PSMA3 trapper-binding proteins have previously been identified as 20S proteasome substrates and, based on published datasets, many of the trapper-binding proteins are associated with the intracellular proteasomes. The PSMA3-trapped IDPs that are proteasome substrates have the unique features previously recognized as characteristic 20S proteasome substrates in vitro. We propose a model whereby the PSMA3 C-terminal region traps a subset of IDPs to facilitate their proteasomal degradation.

pH- and ligand-induced release of loads from DNA-acrylamide hydrogel microcapsules.

Herein, a method to construct stimuli-responsive DNA-acrylamide-based hydrogel microcapsules has been presented. This method involves the use of polyacrylamide chains modified with predesigned nucleic acid hairpin units and optionally single-strand tethers that provide the required hybridization and recognition functions to yield substrate-loaded stimuli-responsive hydrogel-based microcapsules. The synthesis of the microcapsules involves the loading of CaCO3 microparticles with the respective load substrates and the functionalization of the CaCO3 template particles with nucleic acid promoter units. In the presence of the hairpin-modified acrylamide chains, the promoter units induce the hybridization chain reaction (HCR), which leads to the formation of a hydrogel coating, which, after the dissociation of the CaCO3 cores, yields substrate-loaded stimuli-responsive hydrogel microcapsules. One of the microcapsule systems includes, in the hairpin-modified acrylamide constructs, and in the subsequent HCR-generated hydrogel shells, the caged sequences of anti-ATP or anti-cocaine aptamers. In the presence of ATP or cocaine, the duplex-caged aptamer sequences are separated via the formation of ATP- or cocaine-aptamer complexes, which results in the partial separation of the microcapsules and the release of the loads. The second type of microcapsule is cooperatively stabilized by bridges generated by HCR and pH-sensitive duplex units. Under acidic conditions, the pH-sensitive bridges dissociate via the formation of i-motif structures, which results in an increase in the fluidity of the microcapsule shells and the release of the loads. Preliminary studies indicate that ATP- or pH-responsive microcapsules loaded with the anticancer drug, doxorubicin, have a selective cytotoxic effect on MDA-MB-231 cancer cells.

Programmed pH-Responsive Microcapsules for the Controlled Release of CdSe/ZnS Quantum Dots.

Two methods for the preparation of pH-responsive all-DNA microcapsules loaded with CdSe/ZnS quantum dots (QDs) are discussed. One approach involves the construction of DNA microcapsules composed of nucleic acid layers that include, at pH 7.2, "dormant" C-G·C(+) triplex sequences. The formation of the C-G·C(+) triplex structures at pH 5.0 leads to the cleavage of the microcapsules and to the release of the QDs. A second approach involves the synthesis of CdSe/ZnS QD-loaded DNA microcapsules, stabilized at pH 7.2 by T-A·T interlayer triplex bridges. The dissociation of the bridges at pH 9.0 separates the bridging triplex units, resulting in the degradation of the microcapsules and to the release of the QDs. The programmed pH-stimulated release of luminescent QDs, emitting at 620 and 560 nm, from the C-G·C(+) or T-A·T triplex-responsive microcapsules is demonstrated by subjecting the QD-loaded microcapsule mixtures to pH 5.0 or pH 9.0, respectively.