1xg0

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spinqualitylabelsall models 1xg0, resolution 0.97Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

High resolution crystal structure of phycoerythrin 545 from the marine cryptophyte rhodomonas CS24

Overview

Cryptophyte algae differ from cyanobacteria and red algae in the, architecture of their photosynthetic light harvesting systems, even though, all three are evolutionarily related. Central to cryptophyte light, harvesting is the soluble antenna protein phycoerythrin 545 (PE545). The, ultrahigh resolution crystal structure of PE545, isolated from a, unicellular cryptophyte Rhodomonas CS24, is reported at both 1.1A and, 0.97A resolution, revealing details of the conformation and environments, of the chromophores. Absorption, emission and polarized steady state, spectroscopy (298K, 77K), as well as ultrafast (20fs time resolution), measurements of population dynamics are reported. Coupled with, complementary quantum chemical calculations of electronic transitions of, the bilins, these enable assignment of spectral absorption characteristics, to each chromophore in the structure. Spectral differences between the, tetrapyrrole pigments due to chemical differences between bilins, as well, as their binding and interaction with the local protein environment are, described. Based on these assignments, and considering customized optical, properties such as strong coupling, a model for light harvesting by PE545, is developed which explains the fast, directional harvesting of excitation, energy. The excitation energy is funnelled from four peripheral pigments, (beta158,beta82) into a central chromophore dimer (beta50/beta61) in, approximately 1ps. Those chromophores, in turn, transfer the excitation, energy to the red absorbing molecules located at the periphery of the, complex in approximately 4ps. A final resonance energy transfer step, sensitizes just one of the alpha19 bilins on a time scale of 22ps., Furthermore, it is concluded that binding of PE545 to the thylakoid, membrane is not essential for efficient energy transfer to the integral, membrane chlorophyll a-containing complexes associated with PS-II.

About this Structure

1XG0 is a Protein complex structure of sequences from Rhodomonas sp. with CL, MG, DBV and PEB as ligands. Full crystallographic information is available from OCA.

Reference

Developing a structure-function model for the cryptophyte phycoerythrin 545 using ultrahigh resolution crystallography and ultrafast laser spectroscopy., Doust AB, Marai CN, Harrop SJ, Wilk KE, Curmi PM, Scholes GD, J Mol Biol. 2004 Nov 12;344(1):135-53. PMID:15504407

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