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Title: Spectroscopic study of the light-harvesting protein C-phycocyanin associated with colorless linker peptides

Abstract

The phycobilisome (PBS) light-harvesting antenna is composed of chromophore-containing biliproteins and 'colorless' linker peptides and is structurally designed to support unidirectional transfer of excitation energy from the periphery of the PBS to its core. The linker peptides have a unique role in this transfer process by modulating the spectral properties of the associated biliprotein. There is only one three-dimensional structure of a biliprotein/linker complex available to date (APC/LC7.8) and the mechanism of interaction between these two proteins remains unknown. This study brings together a detailed spectroscopic characterization of C-Phycocyanin (PC)-linker complexes (isolated from Synechococcus sp. PCC 7002) with proteomic analysis of the linker amino acid sequences to produce a model for biliprotein/linker interaction. The amino acid sequences of the rod linkers [L R 8.9, L R 32.3 and L RC 28.5] were examined to identify evolutionarily conserved regions important to either the structure or function of this protein family. Although there is not one common homologous site among all the linkers, there are strong trends across each separate subset (L C, L R and L RC) and the N-terminal segments of both L R 32.3 and L RC 28.5 display multiple regions of similarity with other linkers. Predictions of themore » secondary structure of L R 32.3 and L RC 28.5, and comparison to the crystal structure of L C 7.8, further narrowed the candidates for interaction sites with the PC chromophores. Measurements of the absorption, fluorescence, CD and excitation anisotropy of PC trimer, PC/L R 32.3, and PC/L RC 28.5, document the spectroscopic effect of each linker peptide on the PC chromophores at a series of temperatures (298 to 77 K). Because L R 32.3 and L RC 28.5 modulate the PC trimer spectral properties in distinct manners, it suggests different chromophore-interaction mechanisms for each linker. The low temperature absorbance spectrum of the PC trimer is consistent with an excitonic coupling interaction between neighboring a84 and b84 chromophores. Association with LR32.3 does not greatly alter this band shape but the absorbance of the PC/L RC 28.5 complex is dramatically different. This indicates that L RC 28.5 is disrupting the a84 - b84 relation established in the PC trimer. From these, and other polarized spectroscopy measurements, we conclude that both L R 32.3 and L RC 28.5 affect the spectral properties of the terminally emitting PC trimer chromophore (b84), and that L RC 28.5 is additionally perturbing the relationship between the a84 and b84 chromophores to either disrupt or enhance their coupling interaction. The linker can perturb the PC chromophores through either specific aromatic residues or a concentration of electrostatically charged residues. Structurally, the linker disrupts the C3 symmetry of the associated biliprotein and this asymmetric interaction can serve to guide the transfer of excitation energy in one direction.« less

Authors:
 [1]
  1. Univ. of California, Berkeley, CA (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
764396
Report Number(s):
LBNL-45998
R&D Project: 448111; TRN: US200311%%271
DOE Contract Number:  
AC03-76SF00098
Resource Type:
Thesis/Dissertation
Resource Relation:
Other Information: TH: Thesis (Ph.D.); Submitted to University of California, Berkeley, CA (US); PBD: 12 May 2000
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 59 BASIC BIOLOGICAL SCIENCES; ABSORPTION; AMINO ACID SEQUENCE; ANISOTROPY; ANTENNAS; AROMATICS; CRYSTAL STRUCTURE; EXCITATION; FLUORESCENCE; PEPTIDES; PHYCOBILISOMES; PROTEINS; RESIDUES; SPECTROSCOPY; SYMMETRY; LIGHT-HARVESTING; PHYCOBILIPROTEIN SPECTROSCOP; CYANOBACTERIA PHOTOSYNTHESIS

Citation Formats

Pizarro, Shelly Ann. Spectroscopic study of the light-harvesting protein C-phycocyanin associated with colorless linker peptides. United States: N. p., 2000. Web. doi:10.2172/764396.
Pizarro, Shelly Ann. Spectroscopic study of the light-harvesting protein C-phycocyanin associated with colorless linker peptides. United States. doi:10.2172/764396.
Pizarro, Shelly Ann. Mon . "Spectroscopic study of the light-harvesting protein C-phycocyanin associated with colorless linker peptides". United States. doi:10.2172/764396. https://www.osti.gov/servlets/purl/764396.
@article{osti_764396,
title = {Spectroscopic study of the light-harvesting protein C-phycocyanin associated with colorless linker peptides},
author = {Pizarro, Shelly Ann},
abstractNote = {The phycobilisome (PBS) light-harvesting antenna is composed of chromophore-containing biliproteins and 'colorless' linker peptides and is structurally designed to support unidirectional transfer of excitation energy from the periphery of the PBS to its core. The linker peptides have a unique role in this transfer process by modulating the spectral properties of the associated biliprotein. There is only one three-dimensional structure of a biliprotein/linker complex available to date (APC/LC7.8) and the mechanism of interaction between these two proteins remains unknown. This study brings together a detailed spectroscopic characterization of C-Phycocyanin (PC)-linker complexes (isolated from Synechococcus sp. PCC 7002) with proteomic analysis of the linker amino acid sequences to produce a model for biliprotein/linker interaction. The amino acid sequences of the rod linkers [LR8.9, LR32.3 and LRC28.5] were examined to identify evolutionarily conserved regions important to either the structure or function of this protein family. Although there is not one common homologous site among all the linkers, there are strong trends across each separate subset (LC, LR and LRC) and the N-terminal segments of both LR32.3 and LRC28.5 display multiple regions of similarity with other linkers. Predictions of the secondary structure of LR32.3 and LRC28.5, and comparison to the crystal structure of LC7.8, further narrowed the candidates for interaction sites with the PC chromophores. Measurements of the absorption, fluorescence, CD and excitation anisotropy of PC trimer, PC/LR32.3, and PC/LRC28.5, document the spectroscopic effect of each linker peptide on the PC chromophores at a series of temperatures (298 to 77 K). Because LR32.3 and LRC28.5 modulate the PC trimer spectral properties in distinct manners, it suggests different chromophore-interaction mechanisms for each linker. The low temperature absorbance spectrum of the PC trimer is consistent with an excitonic coupling interaction between neighboring a84 and b84 chromophores. Association with LR32.3 does not greatly alter this band shape but the absorbance of the PC/LRC28.5 complex is dramatically different. This indicates that LRC28.5 is disrupting the a84 - b84 relation established in the PC trimer. From these, and other polarized spectroscopy measurements, we conclude that both LR32.3 and LRC28.5 affect the spectral properties of the terminally emitting PC trimer chromophore (b84), and that LRC28.5 is additionally perturbing the relationship between the a84 and b84 chromophores to either disrupt or enhance their coupling interaction. The linker can perturb the PC chromophores through either specific aromatic residues or a concentration of electrostatically charged residues. Structurally, the linker disrupts the C3 symmetry of the associated biliprotein and this asymmetric interaction can serve to guide the transfer of excitation energy in one direction.},
doi = {10.2172/764396},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2000},
month = {5}
}

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