Catalytic linkage between caspase activity and proteostasis in Archaea

Area of Science:

• Biochemistry
• Molecular Biology
• Archaea Research

Background:

• The model haloarchaeon, Haloferax volcanii, exhibits high, specific basal caspase activity resembling caspase-4.
• This activity is inhibited by z-VAD-FMK and is distinct from other protease families.
• The cellular roles and responsible proteins for this dominant proteolytic activity remain unknown.

Purpose of the Study:

• To elucidate the cellular roles and identify the protein(s) responsible for the basal caspase activity in H. volcanii.
• To establish the biochemical context and interactive cellular network of this archaeal caspase activity.
• To explore potential links between archaeal caspase activity and stress-related pathways.

Main Methods:

• Biochemical purification and in situ trapping using caspase-targeted covalent inhibitors.
• Genome-enabled proteomics and structural analysis.
• Targeted gene knockouts and canavanine treatment.

Main Results:

• A catalytic linkage was demonstrated between caspase activity and thermosomes, proteasomes, and cdc48b.
• These components form an 'interactase' complex involved in stress-related protein processing.
• The complex is linked to the unfolded protein response (UPR).

Conclusions:

• Novel cellular and biochemical context for archaeal caspase activity has been provided.
• The findings implicate archaeal caspase activity in protein stress and ER-associated degradation.
• This research offers new insights into the evolution and function of caspase-like activities and their relation to UPR in eukaryotes.