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Synthetic OCP heterodimers are photoactive and recapitulate the fusion of two primitive carotenoproteins in the evolution of cyanobacterial photoprotection
Author(s) -
LechnoYossef Sigal,
Melnicki Matthew R.,
Bao Han,
Montgomery Beronda L.,
Kerfeld Cheryl A.
Publication year - 2017
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.13593
Subject(s) - photoprotection , ctd , biology , cyanobacteria , phycobilisome , carotenoid , fusion protein , genetics , gene , microbiology and biotechnology , computational biology , biochemistry , photosynthesis , recombinant dna , oceanography , bacteria , geology
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 OCP 1 from Fremyella diplosiphon and the presumably more primitive OCP 2 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 OCP 1 and OCP 2 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 NTF 2‐like superfamily found across all kingdoms of life.