Complementation of a phycocyanin-bilin lyase from Synechocystis sp. PCC 6803 with a nucleomorph-encoded open reading frame from the cryptophyte Guillardia theta

Philipps-Universität Marburg, Laboratorium für Zellbiologie, Karl-von-Frisch Str,, D-35032 Marburg, Germany.
BMC Plant Biology (Impact Factor: 3.81). 02/2008; 8(1):56. DOI: 10.1186/1471-2229-8-56
Source: PubMed


Cryptophytes are highly compartmentalized organisms, expressing a secondary minimized eukaryotic genome in the nucleomorph and its surrounding remnant cytoplasm, in addition to the cell nucleus, the mitochondrion and the plastid. Because the members of the nucleomorph-encoded proteome may contribute to essential cellular pathways, elucidating nucleomorph-encoded functions is of utmost interest. Unfortunately, cryptophytes are inaccessible for genetic transformations thus far. Therefore the functions of nucleomorph-encoded proteins must be elucidated indirectly by application of methods in genetically accessible organisms.
Orf222, one of the uncharacterized nucleomorph-specific open reading frames of the cryptophyte Guillardia theta, shows homology to slr1649 of Synechocystis sp. PCC 6803. Recently a further homolog from Synechococcus sp. PCC 7002 was characterized to encode a phycocyanin-beta155-bilin lyase. Here we show by insertion mutagenesis that the Synechocystis sp. PCC 6803 slr1649-encoded protein also acts as a bilin lyase, and additionally contributes to linker attachment and/or stability of phycobilisomes. Finally, our results indicate that the phycocyanin-beta155-bilin lyase of Synechocystis sp. PCC 6803 can be complemented in vivo by the nucleomorph-encoded open reading frame orf222.
Our data show that the loss of phycocyanin-lyase function causes pleiotropic effects in Synechocystis sp. PCC 6803 and indicate that after separating from a common ancestor protein, the phycoerythrin lyase from Guillardia theta has retained its capacity to couple a bilin group to other phycobiliproteins. This is a further, unexpected example of the universality of phycobiliprotein lyases.

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    • "Lithium dodecyl sulfate-PAGE (LiDS-PAGE) analysis revealed that the phycobilisome in ΔcpcF had relatively lower amounts of CpcA, CpcB and the linker polypeptide CpcC1, an apparent absence of CpcC2, and more abundant CpcG1 (Fig. 5C). Interestingly, CpcC2 was also absent from phycobilisomes isolated from a Synechocystis phycocyanin β-subunit lyase (cpcT) mutant [23]. The absence of CpcC2 would suggest that no core-distal phycocyanin hexamers were present in the assembled phycobilisomes from the ΔcpcF strain. "
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