Two Novel Phycoerythrin-Associated Linker Proteins in the Marine CyanobacteriumSynechococcussp. Strain WH8102

Abstract

The recent availability of the whole genome of Synechococcus sp. strain WH8102 allows us to have a global view of the complex structure of the phycobilisomes of this marine picocyanobacterium. Genomic analyses revealed several new characteristics of these phycobilisomes, consisting of an allophycocyanin core and rods made of one type of phycocyanin and two types of phycoerythrins (I and II). Although the allophycocyanin appears to be similar to that found commonly in freshwater cyanobacteria, the phycocyanin is simpler since it possesses only one complete set of ␣ and ␤ subunits and two rod-core linkers (CpcG1 and CpcG2). It is therefore probably made of a single hexameric disk per rod. In contrast, we have found two novel putative phycoerythrin-associated linker polypeptides that appear to be specific for marine Synechococcus spp. The first one (SYNW2000) is unusually long (548 residues) and apparently results from the fusion of a paralog of MpeC, a phycoerythrin II linker, and of CpeD, a phycoerythrin-I linker. The second one (SYNW1989) has a more classical size (300 residues) and is also an MpeC paralog. A biochemical analysis revealed that, like MpeC, these two novel linkers were both chromophorylated with phycourobilin. Our data suggest that they are both associated (partly or totally) with phycoerythrin II, and we propose to name SYNW2000 and SYNW1989 MpeD and MpeE, respectively. We further show that acclimation of phycobilisomes to high light leads to a dramatic reduction of MpeC, whereas the two novel linkers are not significantly affected. Models for the organization of the rods are proposed.

Biochemical Bases of Type IV Chromatic Adaptation in Marine Synechococcus spp

“…Extraction of intact PBSs was carried out with 0.75 M phosphate buffer on a sucrose gradient by the classical procedure (33). Purified PBSs were characterized by their absorption spectra using a double-wavelength DW2 spectrophotometer (Aminco Chance, Bogart, GA).…”

“…nm) on a 10-to-20% acrylamide, continuous-gradient lithium dodecyl sulfate (LiDS)-polyacrylamide gel electrophoresis (PAGE) gel as previously described (33). The chromophorylation state of linker polypeptides was visualized under UV excitation after soaking the gel in 20 mM zinc acetate and by Coomassie blue staining.…”

“…Biochemical analysis of isolated phycobiliprotein complexes. The procedure for PBS dissociation and purification of PBPs on isoelectric focusing (IEF) mini-gels was as previously described (33), except that the soluble proteins were suspended in 10 mM phosphate buffer instead of TES [N-tris(hydroxymethyl)-methyl-2-aminoethanesulfonic acid] buffer. After dissociation of the soluble proteome on a continuous sucrose gradient, the PBS dissociation products were loaded on a 6% acrylamide IEF gel containing ampholytes (pH 4 to 6.5; Amersham Biosciences, Orsay, France).…”

“…Each PBP binds one or two types of chromophores (phycobilins) via covalent thioether bonds to cysteinyl residues. In marine Synechococcus species strains, the blue chromophore phycocyanobilin (PCB; wavelength of maximal absorbance [A max ], ϳ620 nm) is bound to AP and PC, the red chromophore phycoerythrobilin (PEB; A max , ϳ550 nm) to PC and to both PEs, and the orange chromophore phycourobilin (PUB; A max , ϳ495 nm) either to PEII only or to both PEI and PEII (25,26,33). More specifically, in the strains examined to date, PEI contains five attachment sites binding PUB and/or PEB chromophores at a PUB/ PEB ratio of either 0:5 or 2:3, whereas PEII contains six chromophore attachment sites and binds PUB and PEB at a PUB/PEB ratio of 2:4 or 4:2, depending on the strain (9, 25).…”

A preliminary analysis of the gene all0012 of Anabaena PCC 7120

“…The solution was homogenized by sonication for 15 min at 200 W. A final concentration of 2% (w/v) Triton X-100 was added and the samples were incubated with stirring at room temperature for 30 min, then centrifuged at 12,000 × g to allow phase separation. Extraction of PBSs was facilitated on a discontinuous sucrose gradient (2.0, 1.0, 0.5, and 0.25 M) by ultracentrifugation at 128,600 × g for 8 h at 4 °C as described previously (Bryant et al, 1979;Six et al, 2005;Shen et al, 2006). The majority of isolated PBSs were recovered from the region extending from the 0.5 and 1.0 M interface into the 1.0 M layer.…”