The archaeal proteasome is regulated by a network of AAA ATPases.

The proteasome is the central machinery for targeted protein degradation in archaea, Actinobacteria, and eukaryotes. In its basic form, it consists of a regulatory ATPase complex and a proteolytic core particle. The interaction between the two is governed by an HbYX motif (where Hb is a hydrophobic residue, Y is tyrosine, and X is any amino acid) at the C terminus of the ATPase subunits, which stimulates gate opening of the proteasomal α-subunits. In archaea, the proteasome-interacting motif is not only found in canonical proteasome-activating nucleotidases of the PAN/ARC/Rpt group, which are absent in major archaeal lineages, but also in proteins of the CDC48/p97/VAT and AMA groups, suggesting a regulatory network of proteasomal ATPases. Indeed, Thermoplasma acidophilum, which lacks PAN, encodes one CDC48 protein that interacts with the 20S proteasome and activates the degradation of model substrates. In contrast, Methanosarcina mazei contains seven AAA proteins, five of which, both PAN proteins, two out of three CDC48 proteins, and the AMA protein, function as proteasomal gatekeepers. The prevalent presence of multiple, distinct proteasomal ATPases in archaea thus results in a network of regulatory ATPases that may widen the substrate spectrum of proteasomal protein degradation.

Crystal structure of a dimeric archaeal cleavage and polyadenylation specificity factor.

Proteins of the metallo-ß-lactamase (MßL) fold form a large superfamily of metallo-hydrolase/oxidoreductases. Members of this family are found in all three domains of life and are involved in a variety of biological functions related to hydrolysis, redox processes, DNA repair and uptake, and RNA processing. We classified the archaeal homologs of this superfamily based on sequence similarity and characterized a subfamily of the Cleavage and Polyadenylation Specificity Factor (CPSF) with an uncommon domain composition: in addition to an extended MßL domain, which accommodates the active site for RNA cleavage, this group has two N-terminal KH domains. Here, we present the crystal structure of a member of this group from Methanosarcina mazei. It reveals a dimerization mode of the MßL domain that has not been observed before and suggests that RNA is bound across the dimer interface, recognized by the KH domains of one monomer, and cleaved at the active site of the other.

Characterization of photosynthetically active duckweed (Wolffia australiana) in vitro culture by Respiration Activity Monitoring System (RAMOS).

The feasibility of oxygen transfer rate (OTR) measurement to non-destructively monitor plant propagation and vitality of photosynthetically active plant in vitro culture of duckweed (Wolffia australiana, Lemnaceae) was tested using Respiration Activity Monitoring System (RAMOS). As a result, OTR proofed to be a sensitive indicator for plant vitality. The culture characterization under day/night light conditions, however, revealed a complex interaction between oxygen production and consumption, rendering OTR measurement an unsuitable tool to track plant propagation. However, RAMOS was found to be a useful tool in preliminary studies for process development of photosynthetically active plant in vitro cultures.