Abstract
Structures of the open-chain tetrapyrrole (bilin) prosthetic groups of the cryptophycean biliproteins phycocyanin 645 (Cr-PC 645; from strain UW374), phycoerythrin 566 (Cr-PE 566; from strain Bermani) and phycoerythrin 545 (Cr-PE 545; from Proteomonas sulcata Hill & Wetherbee) were examined by absorption, 1H NMR spectroscopy, and mass spectrometry. These biliproteins carry the following covalently attached bilins: Cr-PC 645 (alpha subunit) has one mesobiliverdin, (beta subunit), two phycocyanobilins and a doubly linked 15,16-dihydrobiliverdin; Cr-PC 566 (alpha), bilin 584, (beta), phycoerythrobilin and two bilin 584 chromophores (Wedemayer, G.J., Wemmer, D.E., and Glazer, A.N. (1991) J. Biol. Chem. 266, 4731-4741); Cr-PE 545 (alpha) has one 15,16-dihydrobiliverdin and (beta), only phycoerythrobilins. This is the first report of naturally occurring biliproteins carrying either 15,16-dihydrobiliverdin or mesobiliverdin chromophores. Native cryptomonad phycobiliproteins have been classified on the basis of the position of their long wavelength absorption maxima. However, comparison of the bilins of Cr-PE 566 from strain Bermani with those of Cr-PE 566 of strain CBD shows that the two proteins carry different bilins on the alpha subunit. Consequently, the identity of the bilin prosthetic groups on cryptophycean phycobiliproteins cannot be unambiguously inferred from simple inspection of the visible absorption spectra.
Highlights
Structures oftheopen-chaintetrapyrrole the C-3 and C-18 positions on rings A and D of the tetrapyrprostheticgroupsofthecryptophyceanbiliproteins role (1-9)
Comparison Until recently, assignment of the bilin composition of crypof the bilins of Cr-PE 566 from strain Bermani with tophycean phycobiliproteins was based on the belief that the those of Cr-PE 566 of strain CBD shows that thetwo contributions to such spectra from well characterized bilins, proteins carry different bilins on the a subunit
We examine the structures of bilins attached to cryptomonad phycobiliproteins belonging to two different spectroscopicclasses: phycoerythrin 545 (Cr-PE 545) and phycocyanin 645 (Cr-PC 645)
Summary
This study was prompted by the recent discovery of three bilins with hitherto undescribed structures in a single cryptomonad phycobiliprotein, Cr-PE 566 (strain CBD) (1).Prior to this study, the assignment of structures to cryptomonad bilins relied entirely upon the comparison of absorption spectra of the proteins in the native and denatured state with those of cyanobacterial and red algal phycobiliproteins carrying bilins of known structure. Consespectrum of the purified (UW) a-Cys-18-Prl chromopeptide quently, itis possible to assign bilin peptides to specific in 10 mM aqueous trifluoroacetic acid is shown in Fig.; regions of the primary structure on the basis of amino acid peptide (UW) a-Cys-18-Pr2 possessed a similar spectrum compositional data. A-Cys-18-Prlis mesobiliverdin (MBV) linked to the peptide In addition to themain purple peak (Peak XXV, containing through ring A (Fig. 19).Secondary ion mass spectrometry of peptide (UW)P-DiCys-Pe(l&,-Prl), Fig. (panel C) peptides (UW) a-Cys-18-Prl and (UW) a-Cys-18-Pr2 gave shows a pink satellite peak, labeled as Peak XXIV, whose a n m/z ratio of 1006.5 Da and 949.4 Da, respectively Values are in excellent agreement with the masses of 1006.44 Upon standing in room light, the pink chromopeptide turned
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