8OR7
Structure of a far-red induced allophycocyanin from Chroococcidiopsis thermalis sp. PCC 7203
Summary for 8OR7
| Entry DOI | 10.2210/pdb8or7/pdb |
| Descriptor | Allophycocyanin beta subunit apoprotein, Phycocyanin, PHYCOCYANOBILIN, ... (6 entities in total) |
| Functional Keywords | photosynthesis, phycobiliprotein, allophycocyanin, far-red light photoacclimation |
| Biological source | Chroococcidiopsis thermalis More |
| Total number of polymer chains | 4 |
| Total formula weight | 76254.65 |
| Authors | Zhou, L.J.,Hoeppner, A.,Wang, Y.Q.,Zhao, K.H. (deposition date: 2023-04-13, release date: 2024-03-20, Last modification date: 2024-12-11) |
| Primary citation | Zhou, L.J.,Hoppner, A.,Wang, Y.Q.,Hou, J.Y.,Scheer, H.,Zhao, K.H. Crystallographic and biochemical analyses of a far-red allophycocyanin to address the mechanism of the super-red-shift. Photosynth.Res., 162:171-185, 2024 Cited by PubMed Abstract: Far-red absorbing allophycocyanins (APC), identified in cyanobacteria capable of FRL photoacclimation (FaRLiP) and low-light photoacclimation (LoLiP), absorb far-red light, functioning in energy transfer as light-harvesting proteins. We report an optimized method to obtain high purity far-red absorbing allophycocyanin B, AP-B2, of Chroococcidiopsis thermalis sp. PCC7203 by synthesis in Escherichia coli and an improved purification protocol. The crystal structure of the trimer, (PCB-ApcD5/PCB-ApcB2), has been resolved to 2.8 Å. The main difference to conventional APCs absorbing in the 650-670 nm range is a largely flat chromophore with the co-planarity extending, in particular, from rings BCD to ring A. This effectively extends the conjugation system of PCB and contributes to the super-red-shifted absorption of the α-subunit (λ = 697 nm). On complexation with the β-subunit, it is even further red-shifted (λ = 707 nm, λ = 721 nm). The relevance of ring A for this shift is supported by mutagenesis data. A variant of the α-subunit, I123M, has been generated that shows an intense FR-band already in the absence of the β-subunit, a possible model is discussed. Two additional mechanisms are known to red-shift the chromophore spectrum: lactam-lactim tautomerism and deprotonation of the chromophore that both mechanisms appear inconsistent with our data, leaving this question unresolved. PubMed: 38182842DOI: 10.1007/s11120-023-01066-2 PDB entries with the same primary citation |
| Experimental method | X-RAY DIFFRACTION (2.8 Å) |
Structure validation
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