Abstract
Phycocyanin is one of the two phycobiliproteins always found in the Phycobilisome antenna complex. It is always situated at the ends of the peripheral rods, adjacent to the core cylinders composed of allophycocyanin. The basic phycocyanin monomer is an (αβ) dimer of globin-like subunits with three covalently linked phycocyanobilin cofactors. Monomers assemble further into trimers, hexamers, and rods which include non-pigmented linker proteins. Upon isolation in low ionic strength solution, rods quickly disintegrate into phycocyanin trimers, which lose contacts with other phycobiliproteins and with the linker proteins. The trimers, however, are quite stable and only the presence of high concentrations of chaotropic agents (such as urea), very acidic solutions, or elevated temperatures induces monomerization, followed by separation between the subunits. We have recently determined the crystal structures of phycocyanin from the thremophilic cyanobacterium Thermosynechococcus vulcanus in the presence of 2 or 4 M urea, and shown that 4 M urea monomerizes the phycocyanin trimers. In this paper, we will describe the phycocyanin structures in 2 and 4 M urea more completely. By mapping out the urea positions, we describe the structural elements within the trimeric interaction interface that may be interrupted by the presence of 4 M urea. In addition, we also identify what are the structural characteristics that prevent 4 M urea from inducing subunit dissociation.
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Abbreviations
- APC:
-
Allophycocyanin
- GuCl:
-
Gunidinium Hydrochloride
- LP:
-
Linker protein
- PBP:
-
Phycobiliprotein
- PBS:
-
Phycobilisome
- PC:
-
Phycocyanin
- PCB:
-
Phycocyanobilin
- PE:
-
Phycoerythrin
- PEC:
-
Phycoerythrocyanin
- PSII:
-
Photosystem II
- Tv-PBS:
-
T. vulcanus phycobilisome
- Tv-PC-2 MU:
-
T. vulcanus phycocyanin treated with 2 M urea
- Tv-PC-4 MU:
-
T. vulcanus phycocyanin treated with 4 M urea
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Acknowledgments
This work was supported by the US-Israel Bi-National Science Foundation (2009406) and the Israel Science Foundation founded by the Israel Academy of Sciences and Humanities (1576/12). We also acknowledge the support from the Nancy and Stephen Grand Technion Energy Program (GTEP) and The Technion Russell Berrie Nanotechnology Institute (RBNI). We gratefully thank the staff of the European Synchrotron Radiation Facility (beamlines ID-23-1) for provision of synchrotron radiation facilities and assistance.
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Marx, A., Adir, N. Structural characteristics that stabilize or destabilize different assembly levels of phycocyanin by urea. Photosynth Res 121, 87–93 (2014). https://doi.org/10.1007/s11120-014-9996-5
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DOI: https://doi.org/10.1007/s11120-014-9996-5