Biotin synthase is a pyridoxal phosphate-dependent cysteine desulfurase.
Biotin synthase (BioB) is an iron-sulfur dimeric enzyme which catalyzes the last step in biotin synthesis. The reaction consists of the introduction of a sulfur atom into dethiobiotin. It is shown here that BioB displays a significant cysteine desulfurase activity, providing it with the ability to mobilize sulfur from free cysteine. This activity is dependent on pyridoxal 5'-phosphate (PLP) and dithiothreitol and proceeds through a protein-bound persulfide. Like other cysteine desulfurases, BioB binds 1 equiv of PLP. By site-directed mutagenesis, two conserved cysteines, Cys97 and Cys128, are shown to be critical for cysteine desulfuration and are good candidates as the site for a persulfide. Since biotin synthase activity is greatly increased by PLP and cysteine, even though it does not exceed 1 nmol of biotin/nmol of monomer, it is proposed that cysteine desulfuration is intimately linked to biotin synthesis. New scenarios for sulfur insertion into dethiobiotin, in which cysteine persulfides play a key role, are discussed.
Ollagnier-De-Choudens
Sandrine
S
Laboratoire de Chimie et Biochimie des Centres Rédox Biologiques, DRDC-CB, CEA/CNRS/Université Joseph Fourier, UMR 5047, 17, Avenue des Martyrs, 38054 Grenoble Cedex 09, France.
Mulliez
Etienne
E
Hewitson
Kirsty S
KS
Fontecave
Marc
M
D013437:Carbon-Sulfur Lyases; D002384:Catalysis; D008190:Lyases / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D011732:Pyridoxal Phosphate / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet; D013466:Sulfurtransferases / Q000235:genetics / Q000378:metabolism*
D011994:Recombinant Proteins; D011732:Pyridoxal Phosphate; D013466:Sulfurtransferases; C057985:biotin synthetase; D008190:Lyases; D013437:Carbon-Sulfur Lyases; C080546:cysteine desulfurase