10.1184/R1/6103865.v1
Amanda J. Fischer
Amanda J.
Fischer
Nathan C. Rockwell
Nathan C.
Rockwell
Abigail Y. Jang
Abigail Y.
Jang
Lauren A. Ernst
Lauren A.
Ernst
Alan Waggoner
Alan
Waggoner
Yong Duan
Yong
Duan
Hongxing Lei
Hongxing
Lei
J. Clark Lagarias
J. Clark
Lagarias
Multiple roles of a conserved GAF domain tyrosine residue in cyanobacterial and plant phytochromes.
Carnegie Mellon University
2005
Amino Acid Substitution
Arabidopsis
Oxidoreductases
Photochemistry
Phytochrome
Phytochrome B
Protein Structure
Tertiary
Synechocystis
Tyrosine
2005-11-22 00:00:00
Journal contribution
https://kilthub.cmu.edu/articles/journal_contribution/Multiple_roles_of_a_conserved_GAF_domain_tyrosine_residue_in_cyanobacterial_and_plant_phytochromes_/6103865
<p>The phytochrome family of red/far-red photoreceptors has been optimized to support photochemical isomerization of a bound bilin chromophore, a process that triggers a conformational change and modulates biochemical output from the surrounding protein scaffold. Recent studies have established that the efficiency of this photochemical process is profoundly altered by mutation of a conserved tyrosine residue (Tyr176) within the bilin-binding GAF domain of the cyanobacterial phytochrome Cph1 [Fischer, A. J., and Lagarias, J. C. (2004) Harnessing phytochrome's glowing potential, Proc. Natl. Acad. Sci. U.S.A. 101, 17334-17339]. Here, we show that the equivalent mutation in plant phytochromes behaves similarly, indicating that the function of this tyrosine in the primary photochemical mechanism is conserved. Saturation mutagenesis of Tyr176 in Cph1 establishes that no other residue can support comparably efficient photoisomerization. The spectroscopic consequences of Tyr176 mutations also reveal that Tyr176 regulates the conversion of the porphyrin-like conformation of the bilin precursor to a more extended conformation. The porphyrin-binding ability of the Tyr176Arg mutant protein indicates that Tyr176 also regulates the ligand-binding specificity of apophytochrome. On the basis of the hydrogen-bonding ability of Tyr176 substitutions that support the nonphotochemical C15-Z,syn to C15-Z,anti interconversion, we propose that Tyr176 orients the carboxyl side chain of a conserved acidic residue to stabilize protonation of the bilin chromophore. A homology model of the GAF domain of Cph1 predicts a C5-Z,syn, C10-Z,syn, C15-Z,anti configuration for the chromophore and implicates Glu189 as the proposed acidic residue stabilizing the extended conformation, an interpretation consistent with site-directed mutagenesis of this conserved acidic residue.</p>