The Orange Carotenoid Protein of Cyanobacteria - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 6

Synechocystis sp. PCC 6803: NC_000911

1742748 1747748 1752748 1757748 1762748 1767748 1772748 1777748

Orange carotenoid protein
Conserved hypothetical protein ( slr 1964)
OCP N-terminal domain

Nostoc sp. PCC 7120: NC_003272

1339775 1334775 1329775 1324775 1319775 1314775 1309775

OCP C-terminal domain

Nostoc sp. PCC 7120: NC_003272

Hypothetical protein

3831896 3826896 3821896 3816896 3811896 3806896 3801896

Hypothetical protein

Beta carotene ketolase homolog
Hydrolase
High light inducible protein
Other CDS

Thermosynechococcus elongatus BP-1: NC_004113

1336256 1331256 1326256 1321256 1316256 1311256 1306256

Synechococcus sp. WH 8102: NC_005070

1329327 1334327 1339327 1344327 1349327 1354327 1359327 1364327

Synechococcus sp. WH 7803: NC_009481

892637 887637 882637 877637 872637 867637 862637

Synechococcus sp. RCC307: NC_009482

1703876 1708876 1713876 1718876 1723876 1728876 1733876 1738876

Cyanothece sp. CCY0110, unfinished sequence: NZ_AAXW01000001

-7660 -2660 2340 7340 12340 17340 22340 27340

Gloeobacter violaceus PCC 7421: NC_005125

25882 30882 35882 40882 45882 50882 55882 60882

FIGURE 1.1 Representative ortholog neighborhoods for the OCP and OCP N-terminal paralogs. Arrowhead
length is approximately proportional to gene length. (Adapted from Integrated Microbial Genomes, http://img.
jgi.doe.gov/cgi-bin/pub/main.cgi.)

NPQ (Rakhimberdieva et al. 2004) exactly matches the absorption spectrum of the carotenoid,
3 -hydroxyechinenone (Polivka et al. 2005) in the OCP. The OCP is now known to be specii cally

involved in the phycobilisome-associated NPQ and not in other mechanisms affecting the levels of
l uorescence such as state transitions or D1 damage (Wilson et al. 2006). Studies by immunogold
labeling and electron microscopy showed that most of the OCP is present in the interthylakoid cyto-
plasmic region, on the phycobilisome side of the membrane, Figure 1.2 (Wilson et al. 2006). The
existence of an interaction between the OCP and the phycobilisomes and thylakoids was supported
by the co-isolation of the OCP with the phycobilisome-associated membrane fraction (Wilson
et al. 2006, 2007).
In Synechocystis PCC6803 the OCP is constitutively expressed, present even in mutants lack-
ing phycobilisomes (Wilson et al. 2007). Stress conditions (high light, salt stress, iron starvation)
increases the levels of OCP transcripts and proteins (Hihara et al. 2001, Kanesaki et al. 2002,
Fulda et al. 2006, Wilson et al. 2007). Under iron-starvation conditions, blue light also induces a
large reversible l uorescence quenching much greater than in the presence of iron (Cadoret et al.
2004, Bailey et al. 2005, Joshua et al. 2005). It was proposed that the IsiA protein (iron-stress-
induced protein), a chlorophyll-binding protein, was essential in this NPQ process. However, using
Synechocystis PCC6803 mutants lacking IsiA, the OCP or phycobilisomes, it has been recently
demonstrated that in iron-starved cells (as in iron-containing cells), the blue-light-induced l uo-
rescence quenching is associated with the phycobilisomes and with the OCP and not with IsiA
(Rakhimberdieva et al. 2007b, Wilson et al. 2007). In the

′

IsiA mutant a large reversible l uores-
cence quenching was always induced by blue light. Moreover, during iron starvation the increase

Δ