| Carot_N | |||||||||
|---|---|---|---|---|---|---|---|---|---|
 crystal structure of orange carotenoid protein | |||||||||
| Identifiers | |||||||||
| Symbol | Carot_N | ||||||||
| Pfam | PF09150 | ||||||||
| InterPro | IPR015233 | ||||||||
| SCOP2 | 1m98 / SCOPe / SUPFAM | ||||||||
| |||||||||
In molecular biology the orange carotenoid N-terminal domain is a protein domain found predominantly at the N-terminus of the Orange carotenoid protein (OCP), and is involved in non-covalent binding of a carotenoid chromophore. It is unique for being present in soluble proteins, whereas the vast majority of domains capable of binding carotenoids are intrinsic membrane proteins. Thus far, it has exclusively been found in cyanobacteria, among which it is widespread. The domain also exists on its own, in uncharacterized cyanobacterial proteins referred to as "Red Carotenoid Protein" (RCP). The domain adopts an alpha-helical structure consisting of two four-helix bundles.
Orange carotenoid-binding proteins (OCP) were first identified in cyanobacterial species, where they occur associated with phycobilisome in the cellular thylakoid membrane. These proteins function in photoprotection, and are essential for non-photochemical quenching (NPQ). In full-length OCP, the NPQ activity is regulated by photoactivation by strong blue-green light. OCP seems to act as a homodimer, and binds one molecule of 3'-hydroxyechinenone (a ketocarotenoid) and one chloride ion per subunit. The carotenoid binding site is lined with a striking number of methionine residues. The N-terminal domain of OCP is usually accompanied by a C-terminal domain which belongs to the NTF2 superfamily and helps bind the carotenoid. OCP can be proteolytically cleaved into a red form (RCP), which lacks 15 residues from the N-terminus and approximately 150 residues from the C terminus. This domain is implicated in binding the phycobilisome complex, which thereby facilitates thermal dissipation (quenching) of excess absorbed light energy.
See also
References
- Kirilovsky D, Kerfeld CA (Jul 2013). "The Orange Carotenoid Protein: a blue-green light photoactive protein". Photochemical & Photobiological Sciences. 12 (7): 1135–43. doi:10.1039/c3pp25406b. PMID 23396391.
- Kerfeld CA, Sawaya MR, Brahmandam V, Cascio D, Ho KK, Trevithick-Sutton CC, Krogmann DW, Yeates TO (Jan 2003). "The crystal structure of a cyanobacterial water-soluble carotenoid binding protein". Structure. 11 (1): 55–65. doi:10.1016/S0969-2126(02)00936-X. PMID 12517340.
- Wilson A, Ajlani G, Verbavatz JM, Vass I, Kerfeld CA, Kirilovsky D (Apr 2006). "A soluble carotenoid protein involved in phycobilisome-related energy dissipation in cyanobacteria". The Plant Cell. 18 (4): 992–1007. doi:10.1105/tpc.105.040121. PMC 1425857. PMID 16531492.
- Wilson A, Boulay C, Wilde A, Kerfeld CA, Kirilovsky D (Feb 2007). "Light-induced energy dissipation in iron-starved cyanobacteria: roles of OCP and IsiA proteins". The Plant Cell. 19 (2): 656–72. doi:10.1105/tpc.106.045351. PMC 1867334. PMID 17307930.
- Kerfeld CA (2004). "Structure and function of the water-soluble carotenoid-binding proteins of cyanobacteria". Photosynthesis Research. 81 (3): 215–25. doi:10.1023/B:PRES.0000036886.60187.c8. PMID 16034528. S2CID 28232976.
- Wilson A, Gwizdala M, Mezzetti A, Alexandre M, Kerfeld CA, Kirilovsky D (May 2012). "The essential role of the N-terminal domain of the orange carotenoid protein in cyanobacterial photoprotection: importance of a positive charge for phycobilisome binding". The Plant Cell. 24 (5): 1972–83. doi:10.1105/tpc.112.096909. PMC 3442581. PMID 22634762.