Carotenoid production is regulated by the ATP-dependent Lon protease in the extremophilic archaeon Haloferax volcanii

MICAELA CERLETTI; ROBERTO A. PAGGI; ANSGAR POETSCH; ROSANA E. DE CASTRO

Cordoba

Congreso; 16th International Congress of Photobiology; 2014

The extreme halophilic archaea thrive in environments with high salinity (> 2 M) and solar irradiation. They contain red membrane-bound carotenoid pigments, mainly C50-bacterioruberins, which serve as protection against ultraviolet (UV) light [1]. We have previously constructed and characterized a mutant strain of the haloarchaeon Haloferax volcanii which produces suboptimal levels of the ATP-dependent Lon protease. Down-regulation of this protease resulted in outstanding overpigmentation of the cells (16-fold) while its overexpression turned the cells colourless [2]. This enzyme is conserved across all domains of life and has been thoroughly characterized in bacteria and eukaryotic cells, however, little is known about its role in Archaea and the endogenous substrates of the membrane-bound archaeal protease are unknown. The aim of this study was to detect and identify potential protein substrates of H. volcanii Lon protease. For this, proteomes of the parent and lon mutant strains were compared at different growth stages. Cytoplasm and membrane proteins were fractionated by SDS-PAGE in first dimension followed by RP-nanoLC-ESI-MS/MS (Orbitrap) of trypsin-digested gel slices in second dimension. At least 108 proteins changed significantly between the wt and mutant strain. Interestingly, one of the proteins that showed the highest increase in abundance in the mutant strain (71-73 fold) was phytoene synthase (HVO_2524), a key enzyme in carotenoid biosynthesis. This result suggests that Lon protease is involved in the regulation of phytoene synthase and, consenquently, pigment content in H. volcanii. Acknowledgments MC acknowledges the EMBO and the Boehringer Ingelheim Fonds for financing her travel and living expenses at Ruhr University Bochum, Germany. Supported by CONICET and UNMDP research grants(Argentina). [1] H.R. Shahmohammadi, E. Asgarani, H. Terato, et al., J. Radiat. Res. 1998, 39: 251-262. [2] M. Cerletti, M. Martínez, M. Giménez, D. Sastre, R. Paggi y R. De Castro, Environ. Microbiol. 2014.