Biochemical and structural characterization of a cysteine desulfurase from the extremely thermophilic eubacterium Fervidobacterium islandicum AW-1

The economic use of native feathers is of great interest in poultry waste management, but the degradation mechanism is still not be fully understood. Toward understanding the processes and the enzymes that conduct them, we sequenced the genome of Fervidobacterium islandicum AW-1 that can degrade native chicken feathers at 70°C, and compared it with that of the closest strain F. nodosum Rt17-B1. Comparative genome analysis allowed us to choose several candidates including cysteine desulfurase (CDS), which may be involved in native feather degradation. Indeed, RNA sequencing data revealed that the transcriptional level of CDS increased by 10-fold higher when F. islandicum AW-1 cells were grown with native feathers than with glucose, indicating that the trafficking and delivery of sulfur by CDS might be responsible for keratin degradation. To further characterize it, the FIAW1_18970 gene encoding CDS was cloned, expressed and purified to homogeneity. The purified recombinant enzyme exhibited maximal activity at 90°C and pH 8 under the assay conditions used. Its apparent K_m, V_max, and k_cat values for L-cysteine as the substrate were 75.0±1.7 µM, 1135.0±11.0 U/mg, 53559.5±518.9 min^-1, respectively. To investigate the molecular basis of this enzyme’s catalytic function, we also determined the crystal structure of CDS at the resolution of 2.30Å. Based on these results, we propose that F. islandicum AW-1 CDS may play an important role in feather degradation by the desulfuration of L-cysteine to yield L-alanine and free sulfur, following the cleavage of cysteine disulfide bonds.