The structure at 2 Å resolution of Phycocyanin from Gracilaria chilensis and the energy transfer network in a PC-PC complex

Phycocyanin is a phycobiliprotein involved in light harvesting and conduction of light to the reaction centers in cyanobacteria and red algae. The structure of C-phycocyanin from Gracilaria chilensis was solved by X-ray crystallography at 2.0 angstrom resolution in space group P2(1). An interaction model between two PC heterohexamers was built, followed by molecular dynamic refinement. The best model showed an inter-hexamer rotation of 23 degrees. The coordinates of a PC heterohexamer (alpha beta)(6) and of the PC-PC complex were used to perform energy transfer calculations between chromophores pairs using the fluorescence resonance energy transfer approach (FRET). Two main intra PC((I)beta(82)(3) -> (I)alpha(84)(1) -> (I)alpha(45)(8) -> (I)beta(82)(6) and (I)beta(135)(3) -> (I)beta(153)(5)) and two main inter PC((I)beta(82)(6) -> (II)beta(82)(3) and (I)beta(153)(5) -> (II)beta(153)(3)) pathways were proposed based on the values of the energy transfer constants calculated for all the chromophore pairs in the hexamer and in the complex. (c) 2006 Elsevier B.V. All rights reserved.