Specificity of archaeal caspase activity in the extreme halophile Haloferax volcanii.

Kay D Bidle,Mansha Seth-Pasricha,Kelly A Bidle

doi:10.1111/1758-2229.12010

Kay D Bidle, Mansha Seth-Pasricha + Show 1 more

Open Access

https://doi.org/10.1111/1758-2229.12010

Copy DOI

Abstract

Caspase-like proteases are key initiators and executioners of programmed cell death (PCD), which is initiated by environmental stimuli and manifests in organisms ranging from unicellular microbes to higher eukaryotes. Archaea had been absent from the caspase inheritance discussion due to a lack of gene homologues. We recently demonstrated extremely high, basal caspase-like catalytic activity in the model haloarcheon, Haloferax volcanii, which was linked to the cellular stress response and was widespread among diverse Archaea. Here, we rigorously tested the catalytic specificity of the observed archaeal caspase-like activities using hydrolytic assays with a diverse suite of protease substrates and inhibitors compared with known model serine and cysteine proteases (trypsin, cathepsin, papain, and human caspase-8). Our experiments demonstrate that exponentially growing H. volcanii possesses a highly specific caspase-like activity that most closely resembles caspase-4, is preferentially inhibited by the pan-caspase inhibitor, zVAD-FMK, and has no cross-reactivity with other known protease families. Our findings firmly root the extremely high levels of caspase-like activity as the dominant proteolytic activity in this extreme haloarcheaon, thereby providing further support for housekeeping functions in Haloarchaea. Given the deep archaeal roots of eukaryotes, we suggest that this activity served as a foundation for stress pathways in higher organisms.

Highlights

Caspases are a family of highly refined, intracellular cysteine proteases that cleave a wide variety of substrate proteins at the C-terminus of an aspartate residue within specific tetrapeptide motifs
A variety of caspases have been identified in different metazoan animals, ranging from Hydra to humans (Thornberry and Lazebnik, 1998; Cikala et al, 1999; Sanmartín et al, 2005) that are key initiators and executioners of programmed cell death (PCD) or apoptosis, a genetically controlled, irreversible form of cell death that elicits specific morphological changes initiated by environmental stimuli (Lockshin and Williams, 1965; Kerr et al, 1972)
PCD was first discovered in multicellular organisms, which use it for development and defence, it has been shown to be a ubiquitous trait throughout nature, spanning diverse prokaryotes, and both unicellular and multicellular eukaryotes

Summary

Introduction

Caspases are a family of highly refined, intracellular cysteine proteases that cleave a wide variety of substrate proteins at the C-terminus of an aspartate residue within specific tetrapeptide motifs. We recently demonstrated that the model haloarcheon, Haloferax volcanii, exhibits very high, caspase-8-like (IETDase) activity and expression of immunoreactive proteins to human caspase-8 antisera, both of which were induced by salt stress and death and were abolished by in vivo addition of a broad-spectrum caspase inhibitor (Bidle et al, 2010).

Results

Conclusion