QM/MM Modeling Highlights the Importance of Steric Effects in the Photoactivation of a Bacteriophytochrome
2015 (English)Manuscript (preprint) (Other academic)
Phytochromes constitute a superfamily of photoreceptor proteins that exist in two forms that absorb red (Pr) and far-red (Pfr) light. The conversion of Pr into Pfr (the biologically active form) is triggered by a Z → E photoisomerization of the bilin chromophore at the C15-C16 bond of the methine bridge between pyrrole rings C and D. Here, we present hybrid quantum mechanics/molecular mechanics (QM/MM) calculations on a highresolution Pr crystal structure of Deinococcus radiodurans bacteriophytochrome to investigate the competition between all possible photoisomerizations at the three different (AB, BC and CD) methine bridges. The results demonstrate that steric interactions with the protein are a key discriminator between the different reaction channels. In particular, it is found that such interactions prevent photoisomerization at any other site than the C15-C16 bond. The tendency of phytochromes to always isomerize at this very bond would thus be explained by steric effects.
Place, publisher, year, edition, pages
Chemical Sciences Physical Chemistry
IdentifiersURN: urn:nbn:se:liu:diva-122744OAI: oai:DiVA.org:liu-122744DiVA: diva2:872566