Archaeal membrane-associated proteases: insights on Haloferax volcanii and other haloarchaea.

Marã­A I Gimã©Nez,Rosana E De Castro,Micaela Cerletti

doi:10.3389/fmicb.2015.00039

Abstract

The function of membrane proteases range from general house-keeping to regulation of cellular processes. Although the biological role of these enzymes in archaea is poorly understood, some of them are implicated in the biogenesis of the archaeal cell envelope and surface structures. The membrane-bound ATP-dependent Lon protease is essential for cell viability and affects membrane carotenoid content in Haloferax volcanii. At least two different proteases are needed in this archaeon to accomplish the posttranslational modifications of the S-layer glycoprotein. The rhomboid protease RhoII is involved in the N-glycosylation of the S-layer protein with a sulfoquinovose-containing oligosaccharide while archaeosortase ArtA mediates the proteolytic processing coupled-lipid modification of this glycoprotein facilitating its attachment to the archaeal cell surface. Interestingly, two different signal peptidase I homologs exist in H. volcanii, Sec11a and Sec11b, which likely play distinct physiological roles. Type IV prepilin peptidase PibD processes flagellin/pilin precursors, being essential for the biogenesis and function of the archaellum and other cell surface structures in H. volcanii.

Highlights

Membrane-associated proteases participate in a variety of processes essential for cell physiology including membrane protein quality control, processing of exported and/or membraneanchored polypeptides, regulatory circuits, cell-signaling, the stress response and assembly of cell surface structures (Akiyama, 2009; Dalbey et al, 2011; Schneewind and Missiakas, 2012; Konovalova et al, 2014)
Like all members of the signal peptidase (SPI) family, archaeal SPIs are serine proteases and based on studies performed in SPI from M. voltae (Ng and Jarrell, 2003) and H. volcanii (Fink-Lavi and Eichler, 2008) the catalytic mechanism of the archaeal SPI homolog seems to rely on a Ser/His/Asp tryad resembling the eukaryotic enzyme
The mutant cells were non-motile and were unable to adhere to a glass surface. These results suggest that PibD is needed for maturation of preflagellins and other type IV pilin-like proteins in H. volcanii

Summary

Introduction

Membrane-associated proteases participate in a variety of processes essential for cell physiology including membrane protein quality control, processing of exported and/or membraneanchored polypeptides, regulatory circuits, cell-signaling, the stress response and assembly of cell surface structures (Akiyama, 2009; Dalbey et al, 2011; Schneewind and Missiakas, 2012; Konovalova et al, 2014). The crystal structures of a number of archaeal membrane proteases have been solved (Methanococcus maripaludis FlaK; Thermococcus onnurineus and Archaeoglobus fulgidus LonB proteolytic domains; S2P transmembrane segments (TMSs) core from Methanococcus jannaschii; MCMJR1 peptidase from Methanoculleus marisnigri) providing valuable structure/function insights on these protease families (see Table 1 for references).

Results

Conclusion