Cysteine Desulfurase-Mediated Sulfur Donation Pathways in Plants and Phototrophic Bacteria

Abstract

Cysteine is the sulfur donor for a number of important cofactor biosynthetic pathways including the synthesis of iron-sulfur clusters, thiamine, biotin and molybdenum cofactor. NifS-like cysteine desulfurase enzymes are key components in these pathways, catalyzing the initial release of S from cysteine. NifS-like enzymes do not work alone but are the first component of a sulfur transfer pathway from cysteine to cofactor. In vivo, NifS-like cysteine desulfurases work in concert with assembly factor proteins to which they transfer the released S and which serve to regulate the cysteine desulfurase activity and orchestrate the delivery of S to downstream targets. In plants, the chloroplast localized iron-sulfur assembly machinery resembles at least in part a machinery that in bacteria is responsible for the synthesis of iron-sulfur clusters under oxidative stress and iron limitation. A similar system operates in photosynthetic bacteria. While we are just beginning to unravel the mechanisms of S-dependent cofactor assembly systems it is already evident that these pathways play pivotal roles in cellular metabolism, and particularly are important to the function of plant plastids.