J. Biol. Chem., Vol. 261, Issue 15, 6790-6796, 05, 1986
Phycobiliprotein-bilin linkage diversity. I. Structural studies on A- and D-ring-linked phycocyanobilins
JE Bishop, JC Lagarias, JO Nagy, RW Schoenleber, H Rapoport, AV Klotz and AN Glazer
Phycocyanobilin (PCB) peptides alpha-1 PCB and beta-2T PCB were obtained by
proteolytic degradation of Synechococcus 6301 C- phycocyanin. These
peptides were found to have the following sequences. alpha-1 PCB
Cys(PCB)-Ala-Arg beta-2T PCB Ile-Thr-Gln-Gly-Asp-Cys(PCB)- Ser-Ala. The
peptides were examined by 1H NMR, circular dichroism spectroscopy, and
secondary ion mass spectrometry. The 1H NMR data confirmed that in each
case the bilin was attached through a single linkage, a thioether bond
between the cysteinyl residue and the tetrapyrrole moiety. Comparison of
the 1H NMR spectra of these peptides with those of appropriate model
compounds showed that the thioether linkage in alpha-1 PCB was to the C-3'
position and that in beta-2T PCB to the C-18' position on the bilin.
Refluxing in neutral methanol under nitrogen led to the release of PCB from
alpha-1 PCB but did not release the D-ring-linked tetrapyrrole from
beta-2T. The above results together with those of an earlier study
(Lagarias, J. C., Glazer, A. N., and Rapoport, H. (1979) J. Am. Chem. Soc.
101, 5030-5037) complete the determination of the mode of linkage of each
of the three bilins on C- phycocyanin; two are linked through ring A and
one through ring D. This is the first documented report of a singly
D-ring-linked bilin.
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