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J. Biol. Chem., Vol. 281, Issue 26, 17768-17778, June 30, 2006

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Identification and Characterization of a New Class of Bilin Lyase

THE cpcT GENE ENCODES A BILIN LYASE RESPONSIBLE FOR ATTACHMENT OF PHYCOCYANOBILIN TO CYS-153 ON THE -SUBUNIT OF PHYCOCYANIN IN SYNECHOCOCCUS SP. PCC 7002^*

Gaozhong Shen, Nicolle A. Saunée, Shervonda R. Williams, Eduardo F. Gallo, Wendy M. Schluchter, and Donald A. Bryant¹

From the Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802 and the Department of Biological Sciences, University of New Orleans, New Orleans, Louisiana 70148

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.

Received for publication, March 20, 2006 , and in revised form, April 26, 2006.

^* This work was supported in part by National Science Foundation Grants MCB-0133441 (to W. M. S.) and MCB-0077586 (to D. A. B.). The W. M. Keck Foundation located in the Keck Conservation and Molecular Genetics laboratory at the University of New Orleans provided support for equipment utilized for this study. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains Figs. S1–S5.

¹ Supported by National Institutes of Health Grant GM-31625. To whom correspondence should be addressed. Tel.: 814-865-1992; Fax: 814-863-7024; E-mail: dab14{at}psu.edu.

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