NifS, a pyridoxal 5’-phosphate (PLP) -dependent enzyme which catalyzes the desulforization of L-cysteine to yield L-alanine and elemental sulfur, has a role in the formation of the metallocluster of nitrogenase in Azotobacter vinelandii. Genes with sequence similarity to nifS have been found in various organisms. Synechocystis sp. PCC6803 contains two nifS-like genes, slr0387 and sll0704. We cloned these nifS-like genes, and overexpressed them in Escherichia coli. We purified and characterized their gene products, which were named SsCsd1 and SsCsd2. These enzymes acted on L-selenocysteine,L-cysteine sulfinic acid, and L-cysteine. The activities of the enzymes with L-selenocysteine and L-cysteine sulfinic acid were enhanced by pyruvic acid. The ability to reconstitute iron-sulfur cluster of ferredoxin from Spirulina sp. was examined in vitro. The apoferredoxin was converted to holoferredoxin by SsCsd1 and SsCsd2 in the presence of L-cysteine, ammonium iron (II) sulfate, PLP and dithiothreitol. The result suggests that these cysteine desulfurases play a role in the biosynthesis and repair of iron-sulfur clusters in Synechocystis sp. PCC6803.
