03. Our Cells’ Circadian Clocks
Brian Crane
Brian R. Crane, Chemistry and Chemical Biology, and research colleagues explained the biological mechanism that allows circadian clocks to sense light through a process that transfers energy from light to chemical reactions in cells. Circadian clocks in cells respond to differences in light between night and day allowing organisms to anticipate changes in the environment by pacing their metabolism to this daily cycle. Circadian clocks help determine processes such as when blooming plants open and close their petals, when humans sleep and wake, and when fungi release spores to maximize reproduction. The researchers studied a fungus (Neurospora crassa) and discovered how it uses circadian clock light sensors to control production of carotenoids, which protect against damage from the sun’s ultraviolet radiation after sunrise. They focused on a vivid protein, which contains a chromophore—a light-absorbing molecule. The chromophore captures a photon or particle of light, and the captured energy from the light triggers a series of interactions that ultimately lead to conformational changes on the surface of the vivid protein. These structural changes on the protein’s surface start a series of events affecting the expression of genes, such as those that turn carotenoid production on and off. A similar “switch” may be responsible for timing the sleep cycle in humans. Disruptions of circadian rhythms can cause jet lag, mental illness, and even some forms of cancer.