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The function of selenocysteine synthase and SELB in the synthesis and incorporation of selenocysteine

1991; Elsevier BV; Volume: 73; Issue: 12 Linguagem: Inglês

10.1016/0300-9084(91)90181-y

1638-6183

Karl Forchhammer, K. Boesmiller, August Böck,

Folate and B Vitamins Research

The selAB operon codes for the proteins selenocysteine synthase and SELB which catalyse the synthesis and co-translational insertion of selenocysteine into protein. This communication deals with the biochemical characterisation of these proteins and in particular with their specific interaction with the selenocysteine-incorporating tRNASec. Selenocysteine synthase catalyses the synthesis of selenocysteyl-tRNASec from seryl-tRNASec in a pyridoxal phosphate-dependent reaction mechanism. The enzyme specifically recognizes the tRNASec molecule; a cooperative interaction between the tRNA binding site and the catalytically active pyridoxal phosphate site is suggested. SELB is an EF-Tu-like protein which specifically complexes selenocysteyl-tRNASec. Interaction with the selenol group of the side chain of the aminoacylated residue is a prerequisite for the formation of a stable SELB·tRNA complex. Mechanistically, this provides the biochemical basis for the exclusive selection of selenocysteyl-tRNASec in the decoding step of a selenocysteine-specific UGA triplet.