This domain is present in cGMP-specific phosphodiesterases, adenylyl and guanylyl cyclases, phytochromes, FhlA and NifA. Adenylyl and guanylyl cyclases catalyse ATP and GTP to the second messengers cAMP and cGMP, respectively, these products up-regul ...
This domain is present in cGMP-specific phosphodiesterases, adenylyl and guanylyl cyclases, phytochromes, FhlA and NifA. Adenylyl and guanylyl cyclases catalyse ATP and GTP to the second messengers cAMP and cGMP, respectively, these products up-regulating catalytic activity by binding to the regulatory GAF domain(s). The opposite hydrolysis reaction is catalysed by phosphodiesterase. cGMP-dependent 3',5'-cyclic phosphodiesterase catalyses the conversion of guanosine 3',5'-cyclic phosphate to guanosine 5'-phosphate. Here too, cGMP regulates catalytic activity by GAF-domain binding. Phytochromes are regulatory photoreceptors in plants and bacteria which exist in two thermally-stable states that are reversibly inter-convertible by light: the Pr state absorbs maximally in the red region of the spectrum, while the Pfr state absorbs maximally in the far-red region. This domain is also found in FhlA (formate hydrogen lyase transcriptional activator) and NifA, a transcriptional activator which is required for activation of most Nif operons which are directly involved in nitrogen fixation. NifA interacts with sigma-54. This domain can bind biliverdine and phycocyanobilin (Matilla et al., FEMS Microbiology Reviews, fuab043, 45, 2021, 1. https://doi.org/10.1093/femsre/fuab043).
Phytochromes are red/far-red photochromic biliprotein photoreceptors which regulate plant development. They are widely represented in both photosynthetic and non-photosynthetic bacteria and are known in a variety of fungi. Although sequence similarit ...
Phytochromes are red/far-red photochromic biliprotein photoreceptors which regulate plant development. They are widely represented in both photosynthetic and non-photosynthetic bacteria and are known in a variety of fungi. Although sequence similarities are low, this domain is structurally related to Pfam:PF01590 [1], which is generally located immediately N-terminal to this domain. Compared with Pfam:PF01590, this domain carries an additional tongue-like hairpin loop between the fifth beta-sheet and the sixth alpha-helix which functions to seal the chromophore pocket and stabilise the photoactivated far-red-absorbing state (Pfr) [1]. The tongue carries a conserved PRxSF motif, from which an arginine finger points into the chromophore pocket close to ring D forming a salt bridge with a conserved aspartate residue [1].
The PAS fold corresponds to the structural domain that has previously been defined as PAS and PAC motifs [4]. The PAS fold appears in archaea, eubacteria and eukarya.
