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The 26S proteasome is a large cellular assembly that mediates the selective degradation of proteins in the nucleus and cytosol and is an established target for anticancer therapeutics. Protein substrates are typically targeted to the proteasome through modification with a polyubiquitin chain, which can be recognized by several proteasome-associated ubiquitin receptors. One of these receptors, RPN13/ADRM1, is recruited to the proteasome through direct interaction with the large scaffolding protein RPN2 within the 19S regulatory particle. To better understand the interactions between RPN13, RPN2, and ubiquitin, we used human proteins to map the RPN13-binding epitope to the C-terminal 14 residues of RPN2, which, like ubiquitin, binds the N-terminal pleckstrin-like receptor of ubiquitin (PRU) domain of RPN13. We also report the crystal structures of the RPN13 PRU domain in complex with peptides corresponding to the RPN2 C terminus and ubiquitin. Through mutational analysis, we validated the RPN2-binding interface revealed by our structures and quantified binding interactions with surface plasmon resonance and fluorescence polarization. In contrast to a previous report, we find that RPN13 binds ubiquitin with an affinity similar to that of other proteasome-associated ubiquitin receptors and that RPN2, ubiquitin, and the deubiquitylase UCH37 bind to RPN13 with independent energetics. These findings provide a detailed characterization of interactions that are important for proteasome function, indicate ubiquitin affinities that are consistent with the role of RPN13 as a proteasomal ubiquitin receptor, and have major implications for the development of novel anticancer therapeutics. [ABSTRACT FROM AUTHOR]

Summary The UCH37 deubiquitylase functions in two large and very different complexes, the 26S proteasome and the INO80 chromatin remodeler. We have performed biochemical characterization and determined crystal structures of UCH37 in complexes with RPN13 and NFRKB, which mediate its recruitment to the proteasome and INO80, respectively. RPN13 and NFRKB make similar contacts to the UCH37 C-terminal domain but quite different contacts to the catalytic UCH domain. RPN13 can activate UCH37 by disrupting dimerization, although physiologically relevant activation likely results from stabilization of a surface competent for ubiquitin binding and modulation of the active-site crossover loop. In contrast, NFRKB inhibits UCH37 by blocking the ubiquitin-binding site and by disrupting the enzyme active site. These findings reveal remarkable commonality in mechanisms of recruitment, yet very different mechanisms of regulating enzyme activity, and provide a foundation for understanding the roles of UCH37 in the unrelated proteasome and INO80 complexes. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) continue to attract increasing interest with respect to their applications as luminescent materials. The ordered structure of the metal-organic complex facilitates the selective integration of PAHs that can be tuned to function cooperatively. Here, a unique highly twisted anthracene-based organoplatinum metallacycle was prepared via coordination-driven selfassembly. Single-crystal X-ray diffraction analysis revealed that the metallacycle was twisted through the cooperation of strong π···π stacking interactions and steric hindrance between two anthracenebased ligands. Notably, the intramolecular twist and aggregation behavior introduced restrictions to the conformational change of anthracenes, which resulted in increased emission intensity of the metallacycle in solution. The emission behaviors and suprastructures based on the highly twisted metallacycle can be modulated by the introduction of different solvents. This study demonstrates that this metallacycle with highly twisted structure is a promising candidate for sensing and bioimaging applications. [ABSTRACT FROM AUTHOR]

A cobalt(I) complex is shown to be capable of both electrocatalytic reduction and hydrogenation of CO2 to formate. Several proposed intermediates are characterized and thus form the basis for a proposed mechanism that allows for the dual reactivity: reduction of CO2via H2 addition, and H+/e− equivalents. The work makes use of a novel tris(phosphino) ligand. When a pendent amine is attached to the ligand, no change in catalytic reactivity is observed. [ABSTRACT FROM AUTHOR]

In search of new anti‐tuberculars compatible with anti‐retroviral therapy we re‐identified amicetin as a lead compound. Amicetin's binding to the 70S ribosomal subunit of Thermus thermophilus (Tth) has been unambiguously determined by crystallography and reveals it to occupy the peptidyl transferase center P‐site of the ribosome. The amicetin binding site overlaps significantly with that of the well‐known protein synthesis inhibitor balsticidin S. Amicetin, however, is the first compound structurally characterized to bind to the P‐site with demonstrated selectivity for the inhibition of prokaryotic translation. The natural product‐ribosome structure enabled the synthesis of simplified analogues that retained both potency and selectivity for the inhibition of prokaryotic translation. [ABSTRACT FROM AUTHOR]

In search of new anti‐tuberculars compatible with anti‐retroviral therapy we re‐identified amicetin as a lead compound. Amicetin's binding to the 70S ribosomal subunit of Thermus thermophilus (Tth) has been unambiguously determined by crystallography and reveals it to occupy the peptidyl transferase center P‐site of the ribosome. The amicetin binding site overlaps significantly with that of the well‐known protein synthesis inhibitor balsticidin S. Amicetin, however, is the first compound structurally characterized to bind to the P‐site with demonstrated selectivity for the inhibition of prokaryotic translation. The natural product‐ribosome structure enabled the synthesis of simplified analogues that retained both potency and selectivity for the inhibition of prokaryotic translation. [ABSTRACT FROM AUTHOR]