title: Hydrophobic Residues near the Bilin Chromophore-Binding Pocket Modulate Spectral Tuning of Insert-Cys Subfamily Cyanobacteriochromes.
abstract: Cyanobacteriochromes (CBCRs) are a subfamily of phytochrome photoreceptors found exclusively in photosynthetic cyanobacteria. Four CBCRs containing a second Cys in the insert region (insert-Cys) have been identified from the nonheterocystous cyanobacterium Microcoleus B353 (Mbr3854g4 and Mbl3738g2) and the nitrogen fixing, heterocystous cyanobacterium Nostoc punctiforme (NpF2164g3 and NpR1597g2). These insert-Cys CBCRs can sense light in the near-UV to orange range, but key residues responsible for tuning their colour sensitivity have not been reported. In the present study, near-UV/Green (UG) photosensors Mbr3854g4 (UG1) and Mbl3738g2 (UG2) were chosen for further spectroscopic analysis of their spectral sensitivity and tuning. Consistent with most dual-Cys CBCRs, both UGs formed a second thioether linkage to the phycocyanobilin (PCB) chromophore via the insert-Cys. This bond is subject to breakage and relinkage during forward and reverse photoconversions. Variations in residues equivalent to Phe that are in close contact with the PCB chromophore D-ring in canonical red/green CBCRs are responsible for tuning the light absorption peaks of both dark and photoproducts. This is the first time these key residues that govern light absorption in insert-Cys family CBCRs have been identified and characterised.
authors.affiliation: Department of Biological Sciences, Chungnam National University, Daejeon 34134 Korea.
authors.forename: Sung Mi
authors.initials: SM
authors.lastname: Cho
authors.affiliation: Center for Advanced Measurement and Instrumentation, Korea Research Institute of Standards and Science, Daejeon 34113 Korea.
authors.forename: Sae Chae
authors.initials: SC
authors.lastname: Jeoung
authors.affiliation: Department of Biological Sciences, Chungnam National University, Daejeon 34134 Korea.
authors.forename: Ji-Young
authors.initials: JY
authors.lastname: Song
authors.affiliation: Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34141 Korea.
authors.forename: Ji-Joon
authors.initials: JJ
authors.lastname: Song
authors.affiliation: Department of Biological Sciences, Chungnam National University, Daejeon 34134 Korea.
authors.forename: Youn-Il
authors.initials: YI
authors.lastname: Park
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002942:Circular Dichroism; D017124:Conserved Sequence; D003545:Cysteine / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D020283:Photoreceptors, Microbial / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; D003545:Cysteine