The C-terminal region of phytoene synthase is a key element to control carotenoid biosynthesis in the haloarchaeon Haloferax volcanii

: Cerletti Micaela, Rabino Agustin, Paggi Roberto A, Ferrari Celeste, Poetsch Ansgar, Savilahti Harri, Kiljunen Saija, De Castro Rosana E

Publisher: PORTLAND PRESS LTD

: 2022

: Biochemical Journal

: BIOCHEMICAL JOURNAL

: BIOCHEM J

: 479

: 22

: 2365

: 2377

: 13

: 0264-6021

DOI: https://doi.org/10.1042/BCJ20220403

: https://doi.org/10.1042/BCJ20220403

Phytoene synthase (PSY) converts two molecules of geranyl-geranyl diphosphate to phy-toene, the key regulatory step in carotenogenesis. However, post-translational mechan-isms that control PSY expression are scarcely understood. Carotenoid biosynthesis (mainly bacterioruberin) is a distinctive feature of haloarchaea thriving in hypersaline envir-onments. Carotenogenesis is negatively regulated by the AAA+ LonB protease in the haloarchaeon Haloferax volcanii as it controls PSY degradation. We investigated the rele-vance of the C-terminal portion of HvPSY as a regulatory element for carotenoid biosyn-thesis. H. volcanii mutants were constructed to express full-length HvPSY protein (strain HVPSYwt) and truncated HvPSY lacking 10 (HVPSY10), 20 (HVPSY20) or 34 amino acids (HVPSY34) at the C-terminus. Cells of HVPSY20 and HVPSY34 showed hyperpigmenta-tion (bacterioruberin content 3-fold higher than HVPSYwt) which correlated with increased PSY protein abundance (2-fold in HVPSY34) while they contained less psy transcript level compared with HVPSYwt. In vivo degradation assays showed that HvPSY34 was more stable than HvPSYwt. Collectively, these results show that the C -ter-minal region of HvPSY contains a 'recognition determinant' for proteolysis in H. volcanii. Preliminary evidence suggests that LonB is involved in the recognition mechanism. This study provides the first identification of a regulatory sequence in an archaeal PSY for the post-translational control of carotenogenesis.