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Steric Effects Govern the Photoactivation of Phytochromes
Author(s) -
Falklöf Olle,
Durbeej Bo
Publication year - 2016
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201501080
Subject(s) - photoisomerization , tetrapyrrole , steric effects , chemistry , chromophore , phytochrome , isomerization , photochemistry , stereochemistry , red light , catalysis , organic chemistry , botany , biology , enzyme
Phytochromes constitute a superfamily of photoreceptor proteins existing in two forms that absorb red (Pr) and far‐red (Pfr) light. Although it is well‐known that the conversion of Pr into Pfr (the biologically active form) is triggered by a Z → E photoisomerization of the linear tetrapyrrole chromophore, direct evidence is scarce as to why this reaction always occurs at the methine bridge between pyrrole rings C and D. Here, we present hybrid quantum mechanics/molecular mechanics calculations based on a high‐resolution 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 render photoisomerizations at the AB and BC bridges much less probable than photoisomerization at the CD bridge.