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Transient Deprotonation of the Chromophore Affects Protein Dynamics Proximal and Distal to the Linear Tetrapyrrole Chromophore in Phytochrome Cph1
journal contribution
posted on 2020-02-21, 21:48 authored by Maryam Sadeghi, Jens Balke, Constantin Schneider, Soshichiro Nagano, Johannes Stellmacher, Günter Lochnit, Christina Lang, Chris Weise, Jon Hughes, Ulrike AlexievPhytochromes
are biological red/far-red light sensors found in
many organisms. Prototypical phytochromes, including Cph1 from the
cyanobacterium Synechocystis 6803, act as photochemical
switches that interconvert between stable red (Pr)- and metastable
far-red (Pfr)-absorbing states induced by photoisomerization of the
bilin chromophore. The connection between photoconversion and the
cellular output signal involves light-mediated global structural changes
in the interaction between the photosensory module (PAS-GAF-PHY) and
the C-terminal transmitter (output) module, usually a histidine kinase,
as in the case of Cph1. The chromophore deprotonates transiently during
the Pr → Pfr photoconversion in association with extensive
global structural changes required for signal transmission. Here,
we performed equilibrium studies in the Pr state, involving pH titration
of the linear tetrapyrrole chromophore in different Cph1 constructs,
and measurement of pH-dependent structural changes at various positions
in the protein using picosecond time-resolved fluorescence anisotropy.
The fluorescent reporter group was attached at positions 371 (PHY
domain), 305 (GAF domain), and 120 (PAS domain), as well as at sites
in the PAS-GAF bidomain. We show direct correlation of chromophore
deprotonation with pH-dependent conformational changes in the various
domains. Our results suggest that chromophore deprotonation is closely
associated with a higher protein mobility (conformational space) both
in proximal and in distal protein sites, implying a causal relationship
that might be important for the global large protein arrangements
and thus intramolecular signal transduction.
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PASchromophore deprotonates transientlyPHYPhytochrome Cph 1 PhytochromesmodulepH-dependentPAS-GAFchromophore deprotonationPAS-GAF-PHYPfrpicosecond time-resolved fluorescence anisotropyChromophore Affects Protein Dynamics ProximalsiteCph 1proteinLinear Tetrapyrrole ChromophoreGAFphotoconversionintramolecular signal transduction
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