Catherine Drennan

An old cofactor in a new light: Adenosylcobalamin in light-dependent gene regulation

Adenosylcobalamin (AdoCbl, coenzyme B₁₂) is one of Nature’s most complex enzyme cofactors and enables difficult radical chemistry through cleavage of its covalent cobalt-carbon bond. In a recently discovered bacterial pathway, however, AdoCbl is used in a completely new function: it is used as a light sensor in light-dependent gene regulation. In particular, AdoCbl binds to the transcription factor CarH to regulate expression of the carotenoid biosynthetic cluster. Gene expression is only activated upon light exposure, leading to production of ROS-scavenging carotenoids and protection of the cell from light-induced damage. In this seminar, a structure/function analysis of the light-sensing transcription factor CarH will be presented. These crystallographic and mutational studies provide fundamental insight into a new mode of light-dependent gene regulation and expand the biological role of the AdoCbl cofactor.