Structural and biochemical properties of an extreme 'salt-loving' proteasome activating nucleotidase from the archaeon Haloferax volcanii.

In eukaryotes, the 26S proteasome degrades ubiquitinylated proteins in an ATP-dependent manner. Archaea mediate a form of post-translational modification of proteins termed sampylation that resembles ubiquitinylation. Sampylation was identified in Haloferax volcanii, a moderate halophilic archaeon that synthesizes homologs of 26S proteasome subunits including 20S core particles and regulatory particle triple-A ATPases (Rpt)-like proteasome-associated nucleotidases (PAN-A/1 and PAN-B/2).

Phosphorylation and methylation of proteasomal proteins of the haloarcheon Haloferax volcanii.

Proteasomes are composed of 20S core particles (CPs) of alpha- and beta-type subunits that associate with regulatory particle AAA ATPases such as the proteasome-activating nucleotidase (PAN) complexes of archaea. In this study, the roles and additional sites of post-translational modification of proteasomes were investigated using the archaeon Haloferax volcanii as a model. Indicative of phosphorylation, phosphatase-sensitive isoforms of alpha1 and alpha2 were detected by 2-DE immunoblot.

Hydrophobic carboxy-terminal residues dramatically reduce protein levels in the haloarchaeon Haloferax volcanii.

Proteolysis is important not only to cell physiology but also to the successful development of biocatalysts. While a wide-variety of signals are known to trigger protein degradation in bacteria and eukaryotes, these mechanisms are poorly understood in archaea, known for their ability to withstand harsh conditions. Here we present a systematic study in which single C-terminal amino acid residues were added to a reporter protein and shown to influence its levels in an archaeal cell.

Effect of proteasome inhibitor clasto-lactacystin-beta-lactone on the proteome of the haloarchaeon Haloferax volcanii.

Proteasomes play key roles in a variety of eukaryotic cell functions, including translation, transcription, metabolism, DNA repair and cell-cycle control. The biological functions of these multicatalytic proteases in archaea, however, are poorly understood. In this study, Haloferax volcanii was used as a model to determine the influence the proteasome-specific inhibitor clasto-lactacystin-beta-lactone (cLbetaL) has on archaeal proteome composition.

Proteasomes from structure to function: perspectives from Archaea.

Insight into the world of proteolysis has expanded considerably over the past decade. Energy-dependent proteases, such as the proteasome, are no longer viewed as nonspecific degradative enzymes associated solely with protein catabolism but are intimately involved in controlling biological processes that span life to death. The proteasome maintains this exquisite control by catalyzing the precisely timed and rapid turnover of key regulatory proteins.

Archaeal proteasomes and other regulatory proteases.

Numerous proteases have been shown to catalyze the precisely-timed and rapid turnover of key cellular proteins. Often these regulatory proteases are either energy-dependent or intramembrane-cleaving. In archaea, two different types of energy-dependent proteases have been characterized: 20S proteasomes associated with proteasome-activating nucleotidases and membrane-associated Lon proteases.

Recombinant production of Zymomonas mobilis pyruvate decarboxylase in the haloarchaeon Haloferax volcanii.

The unusual physiological properties of archaea (e.g., growth in extreme salt concentration, temperature and pH) make them ideal platforms for metabolic engineering.

Analysis of proteasome-dependent proteolysis in Haloferax volcanii cells, using short-lived green fluorescent proteins.

Proteasomes are energy-dependent proteases that are central to the quality control and regulated turnover of proteins in eukaryotic cells. Dissection of this proteolytic pathway in archaea, however, has been hampered by the lack of substrates that are easily detected in whole cells. In the present study, we developed a convenient reporter system by functional expression of a green fluorescent protein variant with C-terminal fusions in the haloarchaeon Haloferax volcanii.

Differential regulation of the PanA and PanB proteasome-activating nucleotidase and 20S proteasomal proteins of the haloarchaeon Haloferax volcanii.

The halophilic archaeon Haloferax volcanii produces three different proteins (alpha1, alpha2, and beta) that assemble into at least two 20S proteasome isoforms. This work reports the cloning and sequencing of two H. volcanii proteasome-activating nucleotidase (PAN) genes (panA and panB).

Proteasomes: perspectives from the Archaea.

The development of whole systems approaches to microbiology (e.g. genomics and proteomics) has facilitated a global view of archaeal physiology.

Archaeal proteasomes: potential in metabolic engineering.

Archaea are a valuable source of enzymes for industrial and scientific applications because of their ability to survive extreme conditions including high salt and temperature. Thanks to advances in molecular biology and genetics, archaea are also attractive hosts for metabolic engineering. Understanding how energy-dependent proteases and chaperones function to maintain protein quality control is key to high-level synthesis of recombinant products.