We present a biochemical and crystallographic characterization of active site mutants of the yeast 20S proteasome with the aim to characterize substrate cleavage specificity, subunit intermediate processing, and maturation. ␤1(Pre3), ␤2(Pup1), and ␤5(Pre2) are responsible for the postacidic, tryptic, and chymotryptic activity, respectively. The maturation of active subunits is independent of the presence of other active subunits and occurs by intrasubunit autolysis. The propeptides of ␤6(Pre7) and ␤7(Pre4) are intermediately processed to their final forms by ␤2(Pup1) in the wild-type enzyme and by ␤5(Pre2) and ␤1(Pre3) in the ␤2(Pup1) inactive mutants. A role of the propeptide of ␤1(Pre3) is to prevent acetylation and thereby inactivation. A gallery of proteasome mutants that contain active site residues in the context of the inactive subunits ␤3(Pup3), ␤6(Pre7), and ␤7(Pre4) show that the presence of Gly-1, Thr1, Asp17, Lys33, Ser129, Asp166, and Ser169 is not sufficient to generate activity.

In this Review, we showcase the fundamental processes of intermolecular and intramolecular singlet fission (SF) as a well-researched topic; furthermore we prioritize the information that is relevant for the implementation...

Singlet fission (SF) is a photophysical downconversion pathway, in which a singlet excitation transforms into two triplet excited states.

ATP sulfurylases (ATPSs) are ubiquitous enzymes that catalyse the primary step of intracellular sulfate activation: the reaction of inorganic sulfate with ATP to form adenosine-5'-phosphosulfate (APS) and pyrophosphate (PPi). With the crystal structure of ATPS from the yeast Saccharomyces cerevisiae, we have solved the first structure of a member of the ATP sulfurylase family. We have analysed the crystal structure of the native enzyme at 1.95 Angstroms resolution using multiple isomorphous replacement (MIR) and, subsequently, the ternary enzyme product complex with APS and PPi bound to the active site. The enzyme consists of six identical subunits arranged in two stacked rings in a D:3 symmetric assembly. Nucleotide binding causes significant conformational changes, which lead to a rigid body structural displacement of domains III and IV of the ATPS monomer. Despite having similar folds and active site design, examination of the active site of ATPS and comparison with known structures of related nucleotidylyl transferases reveal a novel ATP binding mode that is peculiar to ATP sulfurylases.

Herein, we present anew class of singlet fission (SF) materials based on diradicaloids of carbene scaffolds,n amely cyclic (alkyl)(amino)carbenes (CAACs). Our modular approach allows the tuning of two key SF criteria:the steric factor and the diradical character.I nt urn, we modified the energy landscapes of excited states in as ystematic manner to accommodate the needs for SF.W er eport the first example of intermolecular SF in solution by dimer self-assembly at cryogenic temperatures.