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Examining Interactions between Bacterioopsin and Carotenoid Biosynthetic Proteins in the Halophilic Archaeon Halobacterium salinarum
Author(s) -
Plesa Alexandru M.,
Peck Ronald F.
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.873.1
Subject(s) - haloferax volcanii , halobacterium salinarum , bacteriorhodopsin , biochemistry , halophile , cofactor , xanthophyll , haloarchaea , opsin , archaea , integral membrane protein , biology , retinaldehyde , retinal , chemistry , membrane protein , carotenoid , enzyme , rhodopsin , membrane , bacteria , gene , genetics
Microbial opsins are complexes consisting of integral membrane proteins covalently bound to the retinal cofactor. These complexes undergo a conformational change in response to light and serve various functions including signaling and energy conservation. First identified in Archaea, microbial opsins have now been found in all three domains of life. Bacteriorhodopsin (BR), the first microbial opsin described, acts as a light‐driven proton pump in the halophilic Archaeon Halobacterium salinarum. When cellular respiration is inhibited due to low oxygen, BR generates a proton gradient that provides energy for ATP synthesis, active transport, and other cellular activities. Interestingly, it appears that the BO apoprotein itself plays an important role in regulating the production of the retinal cofactor. When not bound to retinal, BO inhibits the activity of lycopene elongase (Lye), an enzyme that catalyzes the committed step in the synthesis of bacterioruberins. Bacterioruberins are 50‐carbon carotenoids that integrate into the plasma membrane and are believed to increase membrane stability under conditions of osmotic stress. Since bacterioruberins have common precursors with retinal, the inhibition of Lye by BO likely acts to promote retinal synthesis at the expense of bacterioruberin synthesis. Haloferax volcanii is closely related to H. salinarum and inhabits similarly salty environments. H. volcanii produces bacterioruberins, but does not express any microbial opsins. We had previously determined that, despite a 65% identity between the two Lye homologs, the H. volcanii Lye is not inhibited by BO. This difference suggests that the two proteins have evolutionarily diverged to better suit the needs of the organisms. To identify the motifs in Lye that allow or prevent inhibition by BO, we constructed hybrid genes that included sections of both H. salinarum and H. volcanii lye . These hybrid genes were then placed into H. salinarum strains in the presence or absence of BO expression. BR and bacterioruberin levels were assayed to analyze the activity of Lye. Preliminary evidence suggests that only a small portion of the H. salinarum gene allows inhibition by BO. We have also begun to explore interactions between microbial opsins and Lye homologs from other organisms. Briefly, opsin and Lye homolog genes were expressed in H. volcanii and bacterioruberin production was monitored. Our initial findings indicate that the opsin from some organisms inhibit the activity of the Lye homolog from the same organism. Overall, our results suggest a widely‐distributed, and previously undescribed, activity for opsins. Support or Funding Information Funding was provided by Colby College and the National Institutes of Health (Grant GM094735).