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J. Biol. Chem., Vol. 281, Issue 50, 38769-38780, December 15, 2006

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Sulfur Mobilization in Cyanobacteria

THE CATALYTIC MECHANISM OF L-CYSTINE C-S LYASE (C-DES) FROM SYNECHOCYSTIS^*

Barbara Campanini, Francesca Schiaretti, Stefania Abbruzzetti, Dorothea Kessler^¶, and Andrea Mozzarelli¹

From the Department of Biochemistry and Molecular Biology and the Department of Physics, University of Parma, 43100 Parma, Italy and ^¶Biochemiezentrum, Universität Heidelberg, Heidelberg D-69120, Germany

Sulfur mobilization represents one of the key steps in ubiquitous Fe-S clusters assembly and is performed by a recently characterized set of proteins encompassing cysteine desulfurases, assembly factors, and shuttle proteins. Despite the evolutionary conservation of these proteins, some degree of variability among organisms was observed, which might reflect functional specialization. L-Cyst(e)ine lyase (C-DES), a pyridoxal 5'-phosphatedependent enzyme identified in the cyanobacterium Synechocystis, was reported to use preferentially cystine over cysteine with production of cysteine persulfide, pyruvate, and ammonia. In this study, we demonstrate that C-DES sequences are present in all cyanobacterial genomes and constitute a new family of sulfur-mobilizing enzymes, distinct from cysteine desulfurases. The functional properties of C-DES from Synechocystis sp. PCC 6714 were investigated under pre-steady-state and steady-state conditions. Single wavelength and rapid scanning stopped-flow kinetic data indicate that the internal aldimine reacts with cystine forming an external aldimine that rapidly decays to a transient quinonoid species and stable tautomers of the -aminoacrylate Schiff base. In the presence of cysteine, the transient formation of a dipolar species precedes the selective and stable accumulation of the enolimine tautomer of the external aldimine, with no formation of the -aminoacrylate Schiff base under reducing conditions. Effective sulfur mobilization from cystine might represent a mechanism that allows adaptation of cyanobacteria to different environmental conditions and to light-dark cycles.

Received for publication, July 26, 2006 , and in revised form, September 15, 2006.

^* This work was supported by the Italian Ministry of University and Research Grant COFIN 2005-2006 (to A. M.). 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.

¹ To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biology, V.le G.P. Usberti 23/A, 43100 Parma, Italy. Tel.: 39-0521-905138; Fax: 39-0521-901515; E-mail: andrea.mozzarelli{at}unipr.it.

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