Possible Interaction: Cysteine and Selenocysteine

“As a result of the physicochemical characteristics of selenium when compared with sulfur, Sec is typically more reactive than Cys while participating in similar reactions, and there are also some qualitative differences in the reactivities between the two amino acids.”

“ Selenocysteine and cysteine partner to form a motif featuring a sulfur–selenium covalent bond in many selenoproteins.”

“Many zinc protein families evolved representatives that lack this metal, whereas selenocysteine in proteins is dynamically exchanged with cysteine.”

“Since selenocysteine is a steric isomer of cysteine , numerous control mechanisms have been developed which prevent cross-intrusion of the elements during biosynthesis and insertion.”

“Mutagenesis of the selenocysteine codon to a cysteine codon produced a protein with lower deiodinase activity.”

“Substitution of cysteine for selenocysteine in Type I deiodinase reduced its sensitivity to inhibition by gold 500-fold.”

“ L-Cysteine (Ki, 1.0 mM) competes with L-selenocysteine (Km, 0.83 mM) to inhibit the enzyme reaction.”

“Significance Substitution of cysteine by selenocysteine is held responsible for the increased performance of many enzymes: The higher activity of [NiFeSe]-hydrogenases compared with their [NiFe] counterparts is often attributed to the Sec replacement of one active-site cysteine ligand.”

“However, selenocysteine has also been found to be misincorporated into a small number of proteins displacing cysteines in previous studies, but such misincorporation has not yet been examined at the proteome level thoroughly.”

“Levels of charging with cysteine are reduced about 50% by the presence of a 40-fold excess of selenocysteine.”

“ Selenocysteine in combination with cysteine is a highly effective protector.”