TY - JOUR
T1 - The structural basis of far-red light absorbance by allophycocyanins
AU - Soulier, Nathan
AU - Bryant, Donald A.
N1 - Funding Information:
DAB gratefully acknowledges support from the U. S. National Science Foundation (MCB-1613022). This research was also conducted under the auspices of the Photosynthetic Antenna Research Center (PARC), an Energy Frontier Research Center funded by the DOE, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC 0001035 (DAB). Molecular graphics and analyses performed with UCSF-Chimera, developed by the Resource for Biocomputing, Visualization, and Informatics at the University of California, San Francisco, were supported by NIH award P410GM103311. The authors would like to thank two anonymous reviewers for their thoughtful reviews and comments that helped us to improve this manuscript. The authors thank Dr. Amy Boal for use of her FPLC system and Gavin Palowitch for performing size-exclusion chromatographic analysis of protein samples.
Funding Information:
DAB gratefully acknowledges support from the U. S. National Science Foundation (MCB-1613022). This research was also conducted under the auspices of the Photosynthetic Antenna Research Center (PARC), an Energy Frontier Research Center funded by the DOE, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC 0001035 (DAB). Molecular graphics and analyses performed with UCSF-Chimera, developed by the Resource for Biocomputing, Visualization, and Informatics at the University of California, San Francisco, were supported by NIH award P410GM103311. The authors would like to thank two anonymous reviewers for their thoughtful reviews and comments that helped us to improve this manuscript. The authors thank Dr. Amy Boal for use of her FPLC system and Gavin Palowitch for performing size-exclusion chromatographic analysis of protein samples.
Publisher Copyright:
© 2020, Springer Nature B.V.
PY - 2021/1
Y1 - 2021/1
N2 - Phycobilisomes (PBS), the major light-harvesting antenna in cyanobacteria, are supramolecular complexes of colorless linkers and heterodimeric, pigment-binding phycobiliproteins. Phycocyanin and phycoerythrin commonly comprise peripheral rods, and a multi-cylindrical core is principally assembled from allophycocyanin (AP). Each AP subunit binds one phycocyanobilin (PCB) chromophore, a linear tetrapyrrole that predominantly absorbs in the orange-red region of the visible spectrum (600–700 nm). AP facilitates excitation energy transfer from PBS peripheral rods or from directly absorbed red light to accessory chlorophylls in the photosystems. Paralogous forms of AP that bind PCB and are capable of absorbing far-red light (FRL; 700–800 nm) have recently been identified in organisms performing two types of photoacclimation: FRL photoacclimation (FaRLiP) and low-light photoacclimation (LoLiP). The FRL-absorbing AP (FRL-AP) from the thermophilic LoLiP strain Synechococcus sp. A1463 was chosen as a platform for site-specific mutagenesis to probe the structural differences between APs that absorb in the visible region and FRL-APs and to identify residues essential for the FRL absorbance phenotype. Conversely, red light-absorbing allophycocyanin-B (AP-B; ~ 670 nm) from the same organism was used as a platform for creating a FRL-AP. We demonstrate that the protein environment immediately surrounding pyrrole ring A of PCB on the alpha subunit is mostly responsible for the FRL absorbance of FRL-APs. We also show that interactions between PCBs bound to alpha and beta subunits of adjacent protomers in trimeric AP complexes are responsible for a large bathochromic shift of about ~ 20 nm and notable sharpening of the long-wavelength absorbance band.
AB - Phycobilisomes (PBS), the major light-harvesting antenna in cyanobacteria, are supramolecular complexes of colorless linkers and heterodimeric, pigment-binding phycobiliproteins. Phycocyanin and phycoerythrin commonly comprise peripheral rods, and a multi-cylindrical core is principally assembled from allophycocyanin (AP). Each AP subunit binds one phycocyanobilin (PCB) chromophore, a linear tetrapyrrole that predominantly absorbs in the orange-red region of the visible spectrum (600–700 nm). AP facilitates excitation energy transfer from PBS peripheral rods or from directly absorbed red light to accessory chlorophylls in the photosystems. Paralogous forms of AP that bind PCB and are capable of absorbing far-red light (FRL; 700–800 nm) have recently been identified in organisms performing two types of photoacclimation: FRL photoacclimation (FaRLiP) and low-light photoacclimation (LoLiP). The FRL-absorbing AP (FRL-AP) from the thermophilic LoLiP strain Synechococcus sp. A1463 was chosen as a platform for site-specific mutagenesis to probe the structural differences between APs that absorb in the visible region and FRL-APs and to identify residues essential for the FRL absorbance phenotype. Conversely, red light-absorbing allophycocyanin-B (AP-B; ~ 670 nm) from the same organism was used as a platform for creating a FRL-AP. We demonstrate that the protein environment immediately surrounding pyrrole ring A of PCB on the alpha subunit is mostly responsible for the FRL absorbance of FRL-APs. We also show that interactions between PCBs bound to alpha and beta subunits of adjacent protomers in trimeric AP complexes are responsible for a large bathochromic shift of about ~ 20 nm and notable sharpening of the long-wavelength absorbance band.
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U2 - 10.1007/s11120-020-00787-y
DO - 10.1007/s11120-020-00787-y
M3 - Article
C2 - 33058014
AN - SCOPUS:85092603221
VL - 147
SP - 11
EP - 26
JO - Photosynthesis Research
JF - Photosynthesis Research
SN - 0166-8595
IS - 1
ER -