Structural, Mechanistic and Genomic Insights into OCP- Mediated Photoprotection - Advances in Botanical Research - page 17

genomes has long been noted, but the lack of either sequence homology
to any characterized protein and of any experimental data for a functional
link to the OCP left the role of this protein enigmatic ( Kerfeld, Alexandre,
et al., 2009 ). When this gene was interrupted, only 20-30% of the lost
fluorescence during the cell incubation under strong light was recovered
( Boulay, Wilson, et al., 2010 ). The slr1964 gene product was then named
'fluorescence recovery protein' (FRP). The FRP is a soluble 12-13 kDa
protein and does not bind a chromophore ( Boulay, Wilson, et al., 2010 ).
Co-immunoprecipitation experiments demonstrated that the FRP interacts
with OCP r ( Boulay, Wilson, et al., 2010 ). In vitro , the presence of the FRP
greatly accelerated the OCP r to OCP o conversion ( Boulay, Wilson, et al.,
2010 ). Experiments carried out with mutated OCPs suggested that the
FRP could act by lowering the energy of activation of the OCP r to OCP o
conversion ( Wilson, Gwizdala, et al., 2012 ). When the FRP is added to
OCP r -phycobilisome complexes, it induces or accelerates the fluorescence
recovery, indicating that it promotes the detachment of OCP from the phy-
cobilisomes ( Gwizdala, Wilson, et al., 2011 ). Crystals of FRP that diffract to
3Å have been reported ( Liu, Shuai, et al., 2011 ) and the 2.7 Å structure has
recently been determined (Kerfeld et al., manuscript in preparation).
6. INSIGHTS FROM GENOMIC DISTRIBUTION
OF COMPONENTS OF THE OCP PHOTOPROTECTIVE
MECHANISM
6.1. Distribution of Genes Encoding the OCP
With the recent completion of a large-scale cyanobacterial sequencing proj-
ect (54 phylogenetically diverse cyanobacterial genomes: Shih et al., submit-
ted), comparative genomics of the OCP/FRP system is poised to contribute
to our understanding of the OCP-mediated photoprotective mechanism.
The potential of genomic information to complement structural and
mechanistic studies of OCP function was already apparent at the time of
the initial structure determination. Kerfeld et al. noted that homologues to
slr1963 were present only in cyanobacteria containing phycobilisomes. Like-
wise, they pointed out the presence of shorter OCP paralogues. A survey
of genomic sequence data to-date (a total of 129 genomes which includes
the 54 new cyanobacterial genomes; Shih et al., submitted) shows that genes
encoding the full-length OCP are found in the majority of cyanobacteria
( Fig. 1.3 ); 90 of 127 total genomes surveyed contain at least one gene for a
full-length OCP. Most of the organisms that lack the OCP are found in the