ReceiverSaini et al. BMC Biology(2019) 17:Page 21 ofABCFig. 13. Predicted structural models of ELF4. The a ELF4 monomer, b ELF4 dimer, and c electrostatic potential surface calculated for the ELF4 dimer. Surface locations colored red and blue represent adverse and positive electrostatic possible, respectivelydomain from the response regulators in the bacterial two-component signaling systems. It lacks a conserved Asp present inside the receiver domains with the bacterial RRs which is phosphorylated by the HPK domain, hence the name pseudoreceiver domain (PsR) [220, 225]. A family of PsRs is also observed within the plant circadian clock (PRRs) [185]. The resolution structure in the PsR of CiKA (PDB 2J48) [226] consists of a doubly wound five-stranded -sheet with five -helices (1 and 5 on 1 face and 2 on the other). CiKA mutants lacking the PsR domain showed important raise in autokinase activity [225]. The interaction between the PsR domain along with the HPK domain of CiKA was analyzed by superimposing a predicted model of CiKA-HPK (applying PDB 2C2A as template [227]) plus the solution structure of CiKA-PsR over the Spo0F po0B complex (PDB 1F51 [228]) crystal structure. The PsR domain physically blocked the Hof the HPK domain, making it unavailable for phosphoryl transfer (Fig. 14a), which explains the function of PsR inside the attenuation of CiKA-HPK autophosphorylation activity [226]. Phopshorylation with the receiver domain within the bacterial RRs results in a conformation modify, an effect that’s almost certainly mediated by the pFructosyl-lysine custom synthesis rotein rotein interaction in CiKA. Like CiKA, KaiA also consists of a pseudo-response receiver domain at the N-terminus. In KaiA homodimers, the interaction between the two protomers occurs by means of the 4-5-5 surface with the PsR domain of 1 subunit using the swapped C-terminal domain with the other [44, 60]. It was expected that CiKA may possibly use the very same PsR surface to mediate protein rotein interactions. The phosphatase activity of CikA is enhanced significantly within the presence of KaiC and KaiB. In vivo, CikA- strains showed high levels of phosphorylated RpaA, indicating CikA promotes dephosphorylation of RpaA [229].Saini et al. BMC Biology(2019) 17:Page 22 ofABFig. 14. Structure from the PsR domain of CiKA. a CiKA-PsR (yellow, PDB 2J48) superimposed around the Spo0F po0B complex (blue and orange, PDB 1F51) depicting the structural distinction in the HPK-PsR domain interaction interface in CiKA and bacterial Spo0F po0B. b The full phytochrome sensory module of Synechocystis 6803 Cph1 (PDB 2VEA). The tongue area is encircled. The N-terminal area is shown in yellow, the PAS domain in pink, the GAF domain in orange, along with the PHY domain in green. The phycocyanobilin (PCB) chromophore is shown in blue stick representationAlso, relative to the gsKaiB, fsKaiB variants showed a threefold boost in phosphatase activity of CikA and suppressed RpaA phosphorylation, suggesting that the uncommon active state KaiB interaction with KaiC activates signaling by means of CikA. Shortened periods of oscillation have been observed in vivo and in vitro in the presence of excess of the pseudo-receiver domain of CikA (PsR-CikA). CikA was proposed to interact physically by means of its pseudo-reciever domain. Also, interactions have been observed for KaiB variants (that adopt the fsKaiB state) and PsR-CikA domain but not for PsR-CikA domain and Atopaxar GPCR/G Protein gsKaiB [88]. To understand the molecular basis of this interaction, a study was undertaken making use of MethylTROSY NMR spectroscopy and this revealed that an i.