Cysteine desulfurase catalyzes the removal of sulfur from cysteine and provides sulfide for the biosynthesis of iron-sulfur proteins. This essential enzyme is widely distributed among pro- and eukaryotes, and a homologous form, designated NifS, is additionally found in nitrogen fixing organisms. In solution the protein exists as a dimer of identical 45-kDa subunits. Pyridoxal phosphate (PLP) is used as a cofactor, but cysteine desulfurase does not appear to be homologous to other PLP enzymes and may represent a new structural class of PLP enzyme. We have cloned, overexpressed, and purified the E. coli enzyme, designated IscS, and are studying its role in assembly and repair of Fe/S cluster proteins.
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