Structural, Mechanistic and Genomic Insights into OCP- Mediated Photoprotection - Advances in Botanical Research - page 9

Figure 1.2 Hidden Markov model logo of the primary structure of the OCP. Absolutely
conserved residues are denoted with stars. Sequence numbering corresponds to that of
Synechocystis OCP. The HMM logo was derived from the multiple sequence alignment
of the primary structures of the OCP. The HMM was built using HMMER (Eddy 1998), and
the logo was visualized using LogoMat-M. (Schuster-Boeckler, J. et al. 2004). For colour
version of this igure, the reader is referred to the online version of this topic.
OCP r accumulation largely depend on light intensity ( Wilson, Punginelli,
et al., 2008 ) and, in a less-pronounced manner, on temperature ( Wilson,
Gwizdala, et al., 2012 ). In vitro , in darkness, OCP r spontaneously converts
to OCP o . This reaction shows strong temperature dependence ( Wilson,
Punginelli, et al., 2008 ).
The OCP r is the active form of the protein that mediates energy and
fluorescence quenching at the level of phycobilisomes ( Gwizdala, Wilson,
et al., 2011 ; Punginelli, Wilson, et al., 2009 ; Wilson, Kinney, et al., 2010 ;
Wilson, Punginelli, et al., 2008 ). The presence of the hydrogen bond-
ing between the carotenoid carbonyl group and the C-terminal domain
of the OCP is essential for photoactivity. In the absence of hECN and
echinenone (ECN), OCP binds zeaxanthin (lacking a keto group) but the
resulting yellow zeaxanthin-OCP protein is not photoactivate and it is
unable to induce fluorescence quenching ( Punginelli, Wilson, et al., 2009 ).
Also, the replacement of either Tyr 201 or Trp 288 by other amino acids
renders the OCP photoinactive and unable to induce photoprotection
( Wilson, Punginelli, et al., 2011 ). In contrast, the hydroxyl group does