Phycobilins of cryptophycean algae. Novel linkage of dihydrobiliverdin in a phycoerythrin 555 and a phycocyanin 645.

Cryptomonad strain IVF2 phycoerythrin 555 carries phycoerythrobilins attached through single thioether bonds at alpha-Cys-18, beta-Cys-82, and beta-Cys-158 and a doubly linked 15,16-dihydrobiliverdin (DBV) at beta-DiCys-50,61 (for sequence numbering, see Sidler, W., Nutt, H., Kumpf, B., Frank, G., Suter, F., Brenzel, A., Wehrmeyer, W., and Zuber, H. (1990) Biol. Chem. Hoppe-Seyler 371, 573-547). Analysis of the beta-DiCys-50,61-linked DBV by 1H homonuclear and 1H-13C heteronuclear NMR spectroscopy establishes that the thioether bond from Cys-50 is to the 3"-carbon of the DBV ring A and that from Cys-61 is to the 18'-carbon of ring D, i.e. the peptide-linked bilin is an 8,12-bis(2-carboxyethyl)-3-(2-(cysteinyl-S)-ethyl)-18-(1-(cysteinyl-S)-e thyl)- 2,7,13,17-tetramethylbiladiene-ab-1,19(16H,21H)-dione. DBV is also present at beta-DiCys-50,61 in cryptomonad strain UW374 phycocyanin 645 (Wedemayer, G. J., Kidd, D. G., Wemmer, D. E., and Glazer, A. N. (1992) J. Biol. Chem. 267, 7315-7331). NMR spectroscopy shows that the thioether bonds to this DBV are also at 3" and 18'. Linkage of tetrapyrroles to polypeptides through the 3"-carbon has not hitherto been reported.