Crystal Structure of Allophycocyanin from Marine Cyanobacterium Phormidium sp. A09DM.
Isolated phycobilisome (PBS) sub-assemblies have been widely subjected to X-ray crystallography analysis to obtain greater insights into the structure-function relationship of this light harvesting complex. Allophycocyanin (APC) is the phycobiliprotein always found in the PBS core complex. Phycocyanobilin (PCB) chromophores, covalently bound to conserved Cys residues of α- and β- subunits of APC, are responsible for solar energy absorption from phycocyanin and for transfer to photosynthetic apparatus. In the known APC structures, heterodimers of α- and β- subunits (known as αβ monomers) assemble as trimer or hexamer. We here for the first time report the crystal structure of APC isolated from a marine cyanobacterium (Phormidium sp. A09DM). The crystal structure has been refined against all the observed data to the resolution of 2.51 Å to Rwork (Rfree) of 0.158 (0.229) with good stereochemistry of the atomic model. The Phormidium protein exists as a trimer of αβ monomers in solution and in crystal lattice. The overall tertiary structures of α- and β- subunits, and trimeric quaternary fold of the Phormidium protein resemble the other known APC structures. Also, configuration and conformation of the two covalently bound PCB chromophores in the marine APC are same as those observed in fresh water cyanobacteria and marine red algae. More hydrophobic residues, however, constitute the environment of the chromophore bound to α-subunit of the Phormidium protein, owing mainly to amino acid substitutions in the marine protein.
BRD School of Biosciences, Vadtal Road, Satellite Campus, Sardar Patel University, Vallabh Vidyanagar, India.
Ravi Raghav
RR
Sonani
Protein Crystallography Section, Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai, India.
Gagan Deep
GD
Gupta
BRD School of Biosciences, Vadtal Road, Satellite Campus, Sardar Patel University, Vallabh Vidyanagar, India.
Datta
D
Madamwar
Protein Crystallography Section, Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai, India.
Vinay
V
Kumar
D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000378:metabolism*; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D045524:Phycobilisomes / Q000378:metabolism; D010798:Phycocyanin / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D016415:Sequence Alignment
D045524:Phycobilisomes; D021122:Protein Subunits; C002497:allophycocyanin; D010798:Phycocyanin