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Solution‐State 15 N NMR Spectroscopic Study of α‐C‐Phycocyanin: Implications for the Structure of the Chromophore‐Binding Pocket of the Cyanobacterial Phytochrome Cph1
Author(s) -
Hahn Janina,
Kühne Ronald,
Schmieder Peter
Publication year - 2007
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/cbic.200700256
Subject(s) - chromophore , phycocyanin , phytochrome , phycocyanobilin , chemistry , protonation , tetrapyrrole , stereochemistry , nuclear magnetic resonance spectroscopy , two dimensional nuclear magnetic resonance spectroscopy , photochemistry , cyanobacteria , organic chemistry , biology , botany , ion , red light , bacteria , genetics , enzyme
The detailed structure of the chromophore‐binding pocket in phytochrome proteins and the structural changes associated with its photocycle are still matters of debate. Insight into the structure and dynamics of the binding pocket has been gained through the comparison of a 15 N NMR spectrum of α‐C‐phycocyanin, which is often used as a model system for the study of phytochromes, with the previously described 15 N NMR spectrum of the cyanobacterial phytochrome Cph1. The former spectrum supports the hypothesis that all four nitrogen atoms of the α‐C‐phycocyanin chromophore are protonated, in analogy with the proposed protonation state for the P r and P fr forms of Cph1. The spectra show that the chromophores in both proteins exhibit a distinct dynamic behavior, as also indicated by a NOESY spectrum of Cph1. Finally, stereochemical arguments and a Cph1 homology model support the hypothesis that the chromophore in Cph1 is most likely in the ZZZssa conformation in the P r form of the protein.