## 3 Results and Discussion  
### BLUF Sequences, Modular Domains and Phylogenetic Analysis  
We assessed the residues that are conserved and important for the substrate specificity in the respective orthologs. The details for each protein sequence and domain architecture are given in Table 1 and Figure 1.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \begin{table}
\begin{tabular}{c c c c c c} \hline BLUF + PsiE +BacS superfamily & WP\_014148160.1 & 3–93 & e\({}^{-42}\) & \
\begin{tabular}{c} _Methylomicrobium_ \\ _alcaliphIUM_ \\ \end{tabular} & NP\({}^{*}\) \\ \hline BLUF + CHD + LRR\_R1 & QSS9F2.1 & 57–136 & e\({}^{-24}\) & _Euglena gracilis_ & NP\({}^{*}\) \\ \cline{3-6} Superfamily & & 468–554 & e\({}^{-27}\) & \\ \hline BLUF + CHD + Med 26\_M & & 98–186 & e\({}^{-19}\) & _Theacmons trahens_ & NP\({}^{*}\) \\ \cline{3-6} Superfamily & & 673–756 & e\({}^{-18}\) & ATCC 50062 & \\ \hline BLUF + PRK11633 + DNA & WP\_048452447.1 & 5–99 & e\({}^{-42}\) &
\begin{tabular}{c} _Methylomicroium_ \\ _tahrariae_ \\ \end{tabular} & NP\({}^{*}\) \\ \hline BLUF + TetR\_C\_11 family + Fer2\_2 superfamily & WP\_058743091.1 & 4–92 & e\({}^{-42}\) & _Curbobacterium citream_ & NP\({}^{*}\) \\ \hline BLUF + GALA + Fungal & & & & & \\ TF MIR & & & & & \\ \hline BLUF + SRPRCC & & & & & \\ Superfamily + RGS & & & & & \\ Superfamily & & & & & \\ \hline BLUF + SRPRCC + BTB + & & & & & \\ DUF35522 Superfamily & & & & & \\ \hline BLUF + SRPRCC + FH2 + & & & & & \\ Drf\_FH1 + PRK13729 + & XP\_002669619.1 & 1971–2050 & e\({}^{-28}\) & _Nagleria gruberi_ & NP\({}^{*}\) \\ SMC\_N & & & & & \\ \hline BLUF + SRPRCC & & & & & \\ Superfamily + RGS & & & & & \\ Superfamily & & & & & \\ \hline BLUF + SRPRCC + BTB + & & & & & \\ DUF35522 Superfamily & & & & & \\ \hline BLUF + SRPRCC + FH2 + & & & & & \\ Drf\_FH1 + PRK13729 + & XP\_002669619.1 & 1971–2050 & e\({}^{-28}\) & _Nagleria gruberi_ & NP\({}^{*}\) \\ SMC\_N & & & & & \\ \hline BLUF - Blue light using flavin; EAL- Glutamine/Alanine/Lucucine; PRK- Phosphoribulokinase; PAS- Per/Arnt/Sim; PBP- Phosphatidylylethanolamine-Binding Protein; CHD- Cyclase homology domain; LRR- Leucine-rich repeats; Med26- Mediator of RNA polymerase II transcription subunit 26; B\({}_{12}\)- Vitamin B\({}_{12}\); DNA pol-DNA polymerase; REC- cheY-homologous receiver domain;ITH-Helix turn helix; Endo-S- Endonuclease3; ANK- Ankyrin repeats; RGS- Regulator of G protein signaling; DUF: Domain of unknown function; RhoGEF: Guanine nucleotide exchange factor for Rho/Rac/Cdc42-like GTPases; GALA- Cd14-like Zn(II)2 Cyse (or C6 zinc) binuclear cluster DNA-binding domain; MHR- Middle homology region; PDZ- PSD95/Dlg1/zo-1; SRPBSC-START/RHO_alpha_C/PITP/Bet_v1/CoxG/Calcligand-binding; BTB- Broad-Complex, Tramtrack and Bric a brac; FHA- Formin Homology 2; Drf- Diapahona related domains; SMC_N- N terminus of structural maintenance of chromosomes. Sequences WP_051596720.1 from _Curbobacterium_ sp. UNCCL17; QSS9F2.1 from _Euglena gracilis_ and XP_013758351.1 from _Tracmons trahens_ ATCC 50062 are strongly predicted to contain two BLUF domains on either side of their respective effector domains. NP\({}^{*}\): Probable modulated function cannot be predicted, but requires a detailed study. \\ \hline \end{tabular}
\end{table} 
Table 1: _Cont._  
Figure 1: Schematic representation of the different blue light using flavin (BLUF) modular domain containing proteins. The accession numbers were taken from National Center for Biotechnology Information (NCBI). The mentioned “AA” indicates the amino acid numbers of the particular BLUF modular protein. The analysis of 34 BLUF sequences revealed that residues forming BLUF catalytic core are conserved throughout for interaction with the flavin chromophore (Figure 2). The amino acids tyrosine (Y), asparagine (N), glutamine (Q), and tryptophan (W) or methionine (M), which are crucial for the photodynamics and photocycle of the BLUF domain, are highly conserved (Figure 2).