4N6S: Crystals Of Cross-linked Stabilized And Functional Phycobilisomes: Only Phycocyanin Rods Contribute To Diffraction

Citation:
Abstract
The major light harvesting complex in cyanobacteria and red algae is the phycobilisome (PBS), comprised of hundreds of seemingly similar chromophores, which are protein bound and assembled in a fashion that enables highly efficient uni-directional energy transfer to reaction centers. The PBS is comprised of a core containing 2-5 cylinders surrounded by 6-8 rods, and a number of models have been proposed describing the PBS structure. One of the most critical steps in the functionality of the PBS is energy transfer from the rod substructures to the core substructure. In this study we compare the structural and functional characteristics of high-phosphate stabilized PBS (the standard fashion of stabilization of isolated complexes) with cross-linked PBS in low ionic strength buffer from two cyanobacterial species, Thermosynechococcus vulcanus and Acaryochloris marina. We show that chemical cross-linking preserves efficient energy transfer from the phycocyanin containing rods to the allophycocyanin containing cores with fluorescent emission from the terminal emitters. However, this energy transfer is shown to exist in PBS complexes of different structures as characterized by determination of a 2.4A structure by X-ray crystallography, single crystal confocal microscopy, mass spectrometry and transmission electron microscopy of negatively stained and cryogenically preserved complexes. We conclude that the PBS has intrinsic structural properties that enable efficient energy transfer from rod substructures to the core substructures without requiring a single unique structure. We discuss the significance of our observations on the functionality of the PBS in vivo.
PDB ID: 4N6SDownload
MMDB ID: 116873
PDB Deposition Date: 2013/10/14
Updated in MMDB: 2014/02
Experimental Method:
x-ray diffraction
Resolution: 2.4  Å
Source Organism:
Similar Structures:
Biological Unit for 4N6S: dodecameric; determined by software (PISA)
Molecular Components in 4N6S
Label Count Molecule
Proteins (12 molecules)
6
C-phycocyanin Alpha Subunit
Molecule annotation
6
C-phycocyanin Beta Subunit
Molecule annotation
Chemicals (18 molecules)
1
18
* Click molecule labels to explore molecular sequence information.

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