The photochemical mechanism of a B12-dependent photoreceptor protein

Roger J. Kutta (), Samantha J. O. Hardman, Linus O. Johannissen, Bruno Bellina, Hanan L. Messiha, Juan Manuel Ortiz-Guerrero, Montserrat Elías-Arnanz, S. Padmanabhan, Perdita Barran, Nigel S. Scrutton and Alex R. Jones ()
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Roger J. Kutta: School of Chemistry, The University of Manchester, Oxford Road
Samantha J. O. Hardman: SYNBIOCHEM, Manchester Institute of Biotechnology, The University of Manchester
Linus O. Johannissen: SYNBIOCHEM, Manchester Institute of Biotechnology, The University of Manchester
Bruno Bellina: School of Chemistry, The University of Manchester, Oxford Road
Hanan L. Messiha: SYNBIOCHEM, Manchester Institute of Biotechnology, The University of Manchester
Juan Manuel Ortiz-Guerrero: Area of Genetics (Unidad Asociada al Instituto de Química Física–Consejo Superior de Investigaciones Científicas), Faculty of Biology, Universidad de Murcia
Montserrat Elías-Arnanz: Area of Genetics (Unidad Asociada al Instituto de Química Física–Consejo Superior de Investigaciones Científicas), Faculty of Biology, Universidad de Murcia
S. Padmanabhan: Instituto de Química Física ‘Rocasolano’, Consejo Superior de Investigaciones Científicas
Perdita Barran: School of Chemistry, The University of Manchester, Oxford Road
Nigel S. Scrutton: SYNBIOCHEM, Manchester Institute of Biotechnology, The University of Manchester
Alex R. Jones: School of Chemistry, The University of Manchester, Oxford Road

Nature Communications, 2015, vol. 6, issue 1, 1-11

Abstract: Abstract The coenzyme B12-dependent photoreceptor protein, CarH, is a bacterial transcriptional regulator that controls the biosynthesis of carotenoids in response to light. On binding of coenzyme B12 the monomeric apoprotein forms tetramers in the dark, which bind operator DNA thus blocking transcription. Under illumination the CarH tetramer dissociates, weakening its affinity for DNA and allowing transcription. The mechanism by which this occurs is unknown. Here we describe the photochemistry in CarH that ultimately triggers tetramer dissociation; it proceeds via a cob(III)alamin intermediate, which then forms a stable adduct with the protein. This pathway is without precedent and our data suggest it is independent of the radical chemistry common to both coenzyme B12 enzymology and its known photochemistry. It provides a mechanistic foundation for the emerging field of B12 photobiology and will serve to inform the development of a new class of optogenetic tool for the control of gene expression.

Date: 2015
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DOI: 10.1038/ncomms8907

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