Browsing by Subject "CarH"

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    B12-based photoreceptors: from structure and function to applications in optogenetics and synthetic biology
    (2019-08) Pérez-Castaño, Ricardo; Elías Arnanz, Montserrat; Padmanabhan Iyer, Subramanian; Genética y Microbiología
    Vitamin B12-based photoreceptor proteins sense ultraviolet (UV), blue or green light using 5´-deoxyadenosylcobalamin (AdoCbl). The prototype of this widespread bacterial photoreceptor family, CarH, controls light-dependent gene expression in photoprotective cellular responses. It represses transcription in the dark by binding to operator DNA as an AdoCbl-bound tetramer, whose disruption by light relieves operator binding to allow transcription. Structures of the "dark" (free and DNA-bound) and "light" CarH states and studies on the unusual AdoCbl photochemistry have provided fundamental insights into these photoreceptors. We highlight these, the plasticity within a conserved mode of action among CarH homologs, their distribution, and their promising applications in optogenetics and synthetic biology.
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    Coenzyme B12-dependent and independent photoregulation of carotenogenesis across Myxococcales
    (Wiley, 2022-01-09) Pérez-Castaño, Ricardo; Bastida-Martínez, Eva; Fernández-Zapata, Jesús; Polanco, María C.; Galbis-Martínez, María L.; Iniesta, Antonio A.; Fontes, Marta; Elías-Arnanz, Montserrat; Padmanabhan Iyer, Subramanian; Genética y Microbiología
    Light-induced carotenogenesis in Myxococcus xan- thus is controlled by the B12-based CarH repressor and photoreceptor, and by a separate intricate path- way involving singlet oxygen, the B12-independent CarH paralogue CarA and various other proteins, some eukaryotic-like. Whether other myxobacteria conserve these pathways and undergo photoregulated carotenogenesis is unknown. Here, comparative ana- lyses across 27 Myxococcales genomes identified carotenogenic genes, albeit arranged differently, with carH often in their genomic vicinity, in all three Myxococcales suborders. However, CarA and its associated factors were found exclusively in suborder Cystobacterineae, with carA-carH invariably in tandem in a syntenic carotenogenic operon, except for Cystobacter/Melittangium, which lack CarA but retain all other factors. We experimentally show B12- mediated photoregulated carotenogenesis in repre- sentative myxobacteria, and a remarkably plastic CarH operator design and DNA binding across Myxococcales. Unlike the two characterized CarH from other phyla, which are tetrameric, Cystobacter CarH (the first myxobacterial homologue amenable to analy- sis in vitro) is a dimer that combines direct CarH-like B12-based photoregulation with CarA-like DNA binding and inhibition by an antirepressor. This study pro- vides new molecular insights into B12-dependent pho- toreceptors. It further establishes the B12-dependent pathway for photoregulated carotenogenesis as broadly prevalent across myxobacteria and its evolu- tion, exclusively in one suborder, into a parallel com- plex B12-independent circuit.