Plants, algae and bacteria respond to light in various manners. The effect of light on the growth of plants is called photomorphogenesis and is regulated by the photoreceptor protein named... Show morePlants, algae and bacteria respond to light in various manners. The effect of light on the growth of plants is called photomorphogenesis and is regulated by the photoreceptor protein named phytochrome. Phytochrome is formed in the dark in its inactive red-absorbing (Pr) state and transformed upon absorption of red light to its physiologically active far-red-absorbing state called Pfr. This switching process is linked to a Z-to-E photoisomerization of its open-chain tetrapyrrole cofactor and is transduced to the protein surface modifying the interaction with other proteins in the signal chain. 1H, 15N and 13C cross polarization MAS NMR was used to investigate at atomic resolution both the Pr and Pfr states as well as the two intermediates of the Pfr-to-Pr reaction, Lumi-F and Meta-F. The Pfr state is characterized by a strong hydrogen-bonding at the carbonyl of ring D which leads to an increase in length and strength of the conjugation of the pi-system. The Pfr-to-Pr conversion occurs in two steps: the C15=C16 double bond is photoisomerized in Lumi-F, the rotation around the C14-C15 single bond takes place during the formation of Meta-F. The signal transduction is linked to a change of hydrogen-bonding interaction at the ring D nitrogen with the protein environment. Show less
