Details

Autor(en) / Beteiligte

• Lechno‐Yossef, Sigal
• Melnicki, Matthew R.
• Bao, Han
• Montgomery, Beronda L.
• Kerfeld, Cheryl A.

Titel

Synthetic OCP heterodimers are photoactive and recapitulate the fusion of two primitive carotenoproteins in the evolution of cyanobacterial photoprotection

Ist Teil von

• The Plant journal : for cell and molecular biology, 2017-08, Vol.91 (4), p.646-656

Ort / Verlag

England: Blackwell Publishing Ltd

Erscheinungsjahr

2017

Quelle

MEDLINE

Beschreibungen/Notizen

• Summary The orange carotenoid protein (OCP) governs photoprotection in the majority of cyanobacteria. It is structurally and functionally modular, comprised of a C‐terminal regulatory domain (CTD), an N‐terminal effector domain (NTD) and a ketocarotenoid; the chromophore spans the two domains in the ground state and translocates fully into the NTD upon illumination. Using both the canonical OCP1 from Fremyella diplosiphon and the presumably more primitive OCP2 paralog from the same organism, we show that an NTD‐CTD heterodimer forms when the domains are expressed as separate polypeptides. The carotenoid is required for the heterodimeric association, assembling an orange complex which is stable in the dark. Both OCP1 and OCP2 heterodimers are photoactive, undergoing light‐driven heterodimer dissociation, but differ in their ability to reassociate in darkness, setting the stage for bioengineering photoprotection in cyanobacteria as well as for developing new photoswitches for biotechnology. Additionally, we reveal that homodimeric CTD can bind carotenoid in the absence of NTD, and name this truncated variant the C‐terminal domain‐like carotenoid protein (CCP). This finding supports the hypothesis that the OCP evolved from an ancient fusion event between genes for two different carotenoid‐binding proteins ancestral to the NTD and CTD. We suggest that the CCP and its homologs constitute a new family of carotenoproteins within the NTF2‐like superfamily found across all kingdoms of life. Significance Statement Photoprotection in many cyanobacteria involves the OCP, a modular, photoactive protein. In this paper we describe an evolutionary mechanism using the two OCP paralogs from Fremyella diplosiphon. We show that the two domains of the OCP interact in the absence of a covalent linkage. Our results establish the foundation for optogenetic applications for this modular protein.