Photosynthesis Research

, Volume 121, Issue 1, pp 87–93 | Cite as

Structural characteristics that stabilize or destabilize different assembly levels of phycocyanin by urea

Regular Paper

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.

Keywords

Photosynthesis Cyanobacteria X-ray crystallography Protein denaturation Complex assembly 

Abbreviations Used

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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Copyright information

© Springer Science+Business Media Dordrecht 2014

Authors and Affiliations

  1. 1.Schulich Faculty of ChemistryTechnion-Israel Institute of Technology TechnionHaifaIsrael

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