title: The Transcription Factor CarH Safeguards Use of Adenosylcobalamin as a Light Sensor by Altering the Photolysis Products.
abstract: The newly discovered light-dependent transcription factor CarH uses adenosylcobalamin as a light sensor to regulate expression of protective genes in bacteria upon exposure to sunlight. This use of adenosylcobalamin is a clever adaptation of a classic enzyme cofactor, taking advantage of its photolabile Co-C bond. However, it is also puzzling in that photolysis of adenosylcobalamin generates the 5'-deoxyadenosyl radical that could damage DNA. Here, using liquid chromatography and spectroscopic techniques, we demonstrate that CarH suppresses release of the 5'-deoxyadenosyl radical and instead effects conversion to a nonreactive 4',5'-anhydroadenosine. In this manner, CarH safeguards use of adenosylcobalamin in light-dependent gene regulation.
authors.affiliation: †Department of Chemistry and ‡Department of Biology and Howard Hughes Medical Institute, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Marco
authors.initials: M
authors.lastname: Jost
authors.affiliation: †Department of Chemistry and ‡Department of Biology and Howard Hughes Medical Institute, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Jeffrey H
authors.initials: JH
authors.lastname: Simpson
authors.affiliation: †Department of Chemistry and ‡Department of Biology and Howard Hughes Medical Institute, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Drennan
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000378:metabolism; D001419:Bacteria / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D003038:Cobamides / Q000378:metabolism*; D008027:Light; D010782:Photolysis; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: C012741:4',5'-anhydroadenosine; D001426:Bacterial Proteins; D003038:Cobamides; D014157:Transcription Factors; C000913:cobamamide; D000241:Adenosine