FÖRSTER TRANSFER CALCULATIONS BASED ON CRYSTAL STRUCTURE DATA FROM Agmenellum quadruplicatum C‐PHYCOCYANIN

Sauer, Kenneth; Scheer, Hugo; Sauer, Peter W.

doi:10.1111/j.1751-1097.1987.tb04790.x

Cited by 105 publications

(105 citation statements)

References 31 publications

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“…The absorbance intensity of P641 is double (Q vis/uv Ϸ 2, Table 2), that of P645, and it also has a much more intense fluorescence (supplemental Fig. S1); its properties, therefore, are approaching those of native PC ␣-subunits (24,25). The chromophores of the two species are nonetheless identical, when judged from denaturation experiments.…”

Section: Resultsmentioning

confidence: 96%

“…These two findings suggest that PecA alone has an (autocatalytic) lyase activity but reacts only slowly with free PCB, without kinetically discernible intermediates. In addition, the product has lower absorption and fluorescence than biliproteins like ␣-CPC containing the PCB-chromophore in the native state (24,25); the chromophore is, therefore, bound in a sub-optimal state.…”

Section: Protein-protein Interactionsmentioning

confidence: 99%

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Biliprotein Chromophore Attachment

Böhm

Endres

Scheer

et al. 2007

Journal of Biological Chemistry

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Biliproteins are post-translationally modified by chromophore addition. In phycoerythrocyanin, the heterodimeric lyase PecE/F covalently attaches phycocyanobilin (PCB) to cysteine-␣84 of the apoprotein PecA, with concomitant isomerization to phycoviolobilin. We found that: (a) PecA adds autocatalytically PCB, yielding a low absorbance, low fluorescence PCB⅐PecA adduct, termed P645 according to its absorption maximum; (b) In the presence of PecE, a high absorbance, high fluorescence PCB⅐PecA adduct is formed, termed P641; (c) PecE is capable of transforming P645 to P641; (d) When in stop-flow experiments, PecA and PecE were preincubated before chromophore addition, a red-shifted intermediate (P650, ‫؍‬ 32 ms) was observed followed by a second, which was blue-shifted (P605, ‫؍‬ 0.5 s), and finally a third (P638, ‫؍‬ 14 s) that yielded the adduct (P641, ‫؍‬ 20 min); (e) The reaction was slower, and P605 was missing, if PecA and PecE were not preincubated; (f) Gel filtration gave no evidence of a stable complex between PecA and PecE; however, complex formation is induced by adding PCB; and (g) A red-shifted intermediate was also formed, but more slowly, with phycoerythrobilin, and denaturation showed that this is not yet covalently bound. We conclude, therefore, that PecA and PecE form a weak complex that is stabilized by PCB, that the first reaction step involves a conformational change and/or protonation of PCB, and that PecE has a chaperone-like function on the chromoprotein.Phycobiliproteins are a family of light-harvesting proteins of cyanobacteria, rhodophytes, and cryptophytes (1-4). The apoproteins are post-translationally modified by regio-and stereoselective chromophore attachment to cysteines. Addition to the cysteine-␣84 of cyanobacterial phycocyanins and phycoerythrins is catalyzed by the heterodimeric E/F-type lyases (5). The first enzyme of this type studied, phycocyanobilin:cysteine-␣84-phycocyanin lyase, from the cyanobacterium, Synechococcus sp. PCC 7002, attaches phycocyanobilin (PCB) 3 to apo-␣-phycocyanin (CpcA) (6). It is encoded by two genes, cpcE and cpcF, located on the phycocyanin (CPC) operon downstream of the two apo-phycocyanin and two linker genes. A similar operon structure has been found in several other organisms, but the respective genes can also be located in other positions (5, 7). The functions of the two subunits are still unclear. Chromophore attachment to the phylogenetically related site on the ␤-subunit, cysteine-␤82, is catalyzed by a single-subunit protein, or mixtures of similar proteins (8, 9), whereas the chromophores are attached autocatalytically in phytochromes (10, 11), allophycocyanin, ApcA (12), and the core-membrane linker, ApcE (13). The situation is complicated by the capacity of apo-phycobiliproteins like CpcA/B to also add chromophores autocatalytically but only slowly and in an error-prone fashion (14 -17).The isomerizing phycoviolobilin:cysteine-␣84-phycoerythrocyanin lyase is a member of the E/F-type lyases, which, in addition to chromophore attachment, ha...

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Section: Resultsmentioning

confidence: 96%

Section: Protein-protein Interactionsmentioning

confidence: 99%

Biliprotein Chromophore Attachment

Böhm

Endres

Scheer

et al. 2007

Journal of Biological Chemistry

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“…The absorption properties of the three PCB chromophores of native PC are well characterized (63)(64)(65). The ␣-84 and ␤-82 PCB chromophores of PC absorb maximally between 617 and 628 nm; the fluorescence emission maximum of the ␤-82 PCB, the terminal fluorescence emitter in PC, lies between 644 and 648 nm (63)(64)(65).…”

Section: Phylogenetic Analysis Of Cpct Andmentioning

confidence: 99%

“…The ␣-84 and ␤-82 PCB chromophores of PC absorb maximally between 617 and 628 nm; the fluorescence emission maximum of the ␤-82 PCB, the terminal fluorescence emitter in PC, lies between 644 and 648 nm (63)(64)(65). The absorbance maximum of the PCB chromophore bound to cysteine ␤153 of PC occurs in the range 594 -600 nm and has a fluorescence emission maximum of 623-629 nm.…”

Section: Phylogenetic Analysis Of Cpct Andmentioning

confidence: 99%

Identification and Characterization of a New Class of Bilin Lyase

Shen

Saunée

Williams

et al. 2006

Journal of Biological Chemistry

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Synechococcus sp. PCC 7002 and all other cyanobacteria that synthesize phycocyanin have a gene, cpcT, that is paralogous to cpeT, a gene of unknown function affecting phycoerythrin synthesis in Fremyella diplosiphon. A cpcT null mutant contains 40% less phycocyanin than wild type and produces smaller phycobilisomes with red-shifted absorbance and fluorescence emission maxima. Phycocyanin from the cpcT mutant has an absorbance maximum at 634 nm compared with 626 nm for the wild type. The phycocyanin ␤-subunit from the cpcT mutant has slightly smaller apparent molecular weight on SDS-PAGE. Purified phycocyanins from the cpcT mutant and wild type were cleaved with formic acid, and the products were analyzed by SDS-PAGE. No phycocyanobilin chromophore was bound to the peptide containing Cys-153 derived from the phycocyanin ␤-subunit of the cpcT mutant. Recombinant CpcT was used to perform in vitro bilin addition assays with apophycocyanin (CpcA/CpcB) and phycocyanobilin. Depending on the source of phycocyanobilin, reaction products with CpcT had absorbance maxima between 597 and 603 nm as compared with 638 nm for the control reactions, in which mesobiliverdin becomes covalently bound. After trypsin digestion and reverse phase high performance liquid chromatography, the CpcT reaction product produced one major phycocyanobilin-containing peptide. This peptide had a retention time identical to that of the tryptic peptide that includes phycocyanobilin-bound, cysteine 153 of wild-type phycocyanin. The results from characterization of the cpcT mutant as well as the in vitro biochemical assays demonstrate that CpcT is a new phycocyanobilin lyase that specifically attaches phycocyanobilin to Cys-153 of the phycocyanin ␤-subunit. Cyanobacteria and red algae contain peripheral, light-harvesting complexes called phycobilisomes (PBS).2 These macromolecular complexes are composed of two types of proteins: colored phycobiliproteins (PBPs), which absorb and transmit light energy to the photosynthetic reaction centers, and non-pigmented linker proteins, which direct the assembly of PBS (1). In many cyanobacteria, including Synechococcus sp. PCC 7002, PBS are composed of two blue-colored PBPs: phycocyanin (PC) and allophycocyanin (AP). These PBPs are composed of two subunits, ␣ and ␤ (2), which are members of the globin superfamily (3). The ␣-and ␤-subunits of PC and AP carry at least one linear tetrapyrrole chromophore (bilin) called phycocyanobilin (PCB), which is covalently attached to specific cysteine residues via thioether linkages (see supplemental Fig. 1) (4). The bilin chromophores of PBPs are derived from heme and are related to the phytochromobilin (5), the photoisomerizable chromophore of the plant protein, phytochrome (6). X-ray crystallographic analyses of PC have shown that the chiral C3 1 carbons of the PCB chromophores attached at cysteines ␣84 and ␤82 are in the R configuration, whereas the C3

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“…the phycobilisomes [ 11. The results obtained on these pigments led investigators to classify the dye molecules as s (sentizing) and f (fluorescing) chromophores [ 561 (for a refined treatment, see ref. [ 71). Naturally, the f chromophore is the dye molecule with the lowest S, energy.…”

Section: Introductionmentioning

confidence: 99%