New function and application of the cysteine synthase from archaea

Proposal of the archaea as a discrete domain shed new light on the central problems of early evolution of life and prokaryotic systematics. Recently new amino acid synthesis pathways and new amino acid synthases have been found in archaea from its genome database. The cysteine biosynthesis of many organisms has been studied well and seems to be a crucial metabolic pathway supplying a building block for de novo protein synthesis. The pathway of cysteine biosynthesis of archaea remains to be elucidated. From the characterization of cysteine synthase of hyperthermophilic archaea Aeropyrum pernix, new enzyme O-phosphoserine sulfhydrylase (OPSS; EC 2.5.1.65) which catalyzes the new reaction of synthesis of cysteine from O-phospho-l-serine and sulfide was found. From the finding of OPSS, new pathway for cysteine synthesis was pointed out in archaea and its application has been expected. The unique substrate specificity and characteristics of OPSS seem to be applicable for many fields. In this review, the application of the enzyme and new cysteine synthesis pathway are discussed together with structural study.