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Title: Light-regulated synthesis of cyclic-di-GMP by a bidomain construct of the cyanobacteriochrome Tlr0924 (SesA) without stable dimerization

Here, phytochromes and cyanobacteriochromes (CBCRs) use double bond photoisomerization of their linear tetrapyrrole (bilin) chromophores within cGMP-specific phosphodiesterases/Adenylyl cyclases/FhlA (GAF) domain-containing photosensory modules to regulate activity of C-terminal output domains. CBCRs exhibit much more diverse photocycles than phytochromes, and are often found in large modular proteins such as Tlr0924 (SesA), one of three blue light regulators of cell aggregation in the cyanobacterium Thermosynechococcus elongatus. Tlr0924 contains a single bilin-binding GAF domain adjacent to a C-terminal diguanylate cyclase (GGDEF) domain whose catalytic activity requires formation of a dimeric transition state presumably supported by a multi-domain extension at its N-terminus. To probe the structural basis of light-mediated signal propagation from the photosensory input domain to a signaling output domain for a representative CBCR, these studies explore the properties of a bidomain GAF-GGDEF construct of Tlr0924 (Tlr0924Δ) that retains light-regulated diguanylate cyclase activity. Surprisingly, CD spectroscopy and size exclusion chromatography data do not support formation of stable dimers in the either the blue-absorbing 15ZP b dark state or the green-absorbing 15EP g photoproduct state of Tlr0924Δ. Analysis of variants containing site-specific mutations reveals that proper signal transmission requires both chromophorylation of the GAF domain and individual residues within the amphipathic linker region betweenmore » GAF and GGDEF domains. Based on these data, we propose a model in which bilin binding and light signals are propagated from the GAF domain via the linker region to alter the equilibrium and interconversion dynamics between active and inactive conformations of the GGDEF domain to favor or disfavor formation of catalytic competent dimers.« less
 [1] ;  [1] ;  [1]
  1. Univ. of California, Davis, CA (United States)
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Grant/Contract Number:
Accepted Manuscript
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Additional Journal Information:
Journal Volume: 56; Journal Issue: 46; Journal ID: ISSN 0006-2960
American Chemical Society (ACS)
Research Org:
Univ. of California, Davis, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
59 BASIC BIOLOGICAL SCIENCES; light harvesting antennae; photoreceptor; biliproteins; photosynthesis; cyanobacteria
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