Selenium is an essential micronutrient with important functions in human health and relevance to several pathophysiological conditions. The biological effects of selenium are largely mediated by se...

https://www.physiology.org/doi/pdf/10.1152/physrev.00039.2013

Selenoproteins: molecular pathways and physiological roles.

Cysteine sulfinate desulfinase, a nifs-like protein of escherichia coli with selenocysteine lyase and cysteine desulfurase activities : gene cloning, purification, and characterization of a novel pyridoxal enzyme

Selenocysteine lyase (EC 4.4.1.16) exclusively decomposes selenocysteine to alanine and elemental selenium, whereas cysteine desulfurase (NIFS protein) of Azotobacter vinelandii acts indiscriminately on both cysteine and selenocysteine to produce elemental sulfur and selenium respectively, and alanine. These proteins exhibit some sequence homology. The Escherichia coli genome contains three genes with sequence homology to nifS. We have cloned the gene mapped at 63.4 min in the chromosome and have expressed, purified to homogeneity, and characterized the gene product. The enzyme comprises two identical subunits with 401 amino acid residues (Mr 43,238) and contains pyridoxal 5'-phosphate as a coenzyme. The enzyme catalyzes the removal of elemental sulfur and selenium atoms from L-cysteine, L-cystine, L-selenocysteine, and L-selenocystine to produce L-alanine. Because L-cysteine sulfinic acid was desulfinated to form L-alanine as the preferred substrate, we have named this new enzyme cysteine sulfinate desulfinase. Mutant enzymes having alanine substituted for each of the four cysteinyl residues (Cys-100, Cys-176, Cys-323, and Cys-358) were all active. Cys-358 corresponds to Cys-325 of A. vinelandii NIFS, which is conserved among all NIFS-like proteins and catalytically essential (Zheng, L., White, R. H., Cash, V. L., and Dean, D. R. (1994) Biochemistry 33, 4714-4720), is not required for cysteine sulfinate desulfinase. Thus, the enzyme is distinct from A. vinelandii NIFS in this respect.

Cysteine Sulfinate Desulfinase, a NIFS-like Protein of Escherichia coli with Selenocysteine Lyase and Cysteine Desulfurase Activities: Gene Cloning, Purification and Characterization of a Novel Pyridoxal Enzyme

Escherichia coli NifS-like Proteins Provide Selenium in the Pathway for the Biosynthesis of Selenophosphate

Escherichia coli CsdB, a NifS homologue with a high specificity for l-selenocysteine, is a pyridoxal 5‘-phosphate (PLP)-dependent dimeric enzyme that belongs to aminotransferases class V in fold-type I of PLP enzymes and catalyzes the decomposition of l-selenocysteine into selenium and l-alanine. The crystal structure of the enzyme has been determined by the X-ray crystallographic method of multiple isomorphous replacement and refined to an R-factor of 18.7% at 2.8 A resolution. The subunit structure consists of three parts:  a large domain of an α/β-fold containing a seven-stranded β-sheet flanked by seven helices, a small domain containing a four-stranded antiparallel β-sheet flanked by three α-helices, and an N-terminal segment containing two α-helices. The overall fold of the subunit is similar to those of the enzymes belonging to the fold-type I family represented by aspartate aminotransferase. However, CsdB has several structural features that are not observed in other families of the enzymes. A rem...

Structure of a NifS homologue: X-ray structure analysis of CsdB, an Escherichia coli counterpart of mammalian selenocysteine lyase

The purification and characterization of bacterial selenocysteine beta-lyase, an enzyme which specifically catalyzes the cleavage of L-selenocysteine to L-alanine and Se0, are presented The enzyme, purified to near homogeneity from Citrobacter freundii, is monomeric with a molecular weight of ca 64,000 and contains 1 mol of pyridoxal 5'-phosphate as a cofactor per mol of enzyme L-Selenocysteine is the sole substrate (Km, 095 mM) L-Cysteine is a competitive inhibitor of the enzyme (Ki, 065 mM) The enzyme also catalyzes the alpha, beta elimination of beta-chloro-L-alanine to form NH3, pyruvate, and Cl- and is irreversibly inactivated during the reaction The physicochemical properties, eg, amino acid composition and subunit structure, of the bacterial enzyme are fairly different from those of the pig liver enzyme (Esaki et al, J Biol Chem 257:4386-4391, 1982) However, the catalytic properties of both enzymes, eg, substrate specificity and inactivation by the substrate or a mechanism-based inactivator, beta-chloro-L-alanine, are very similar

Purification and characterization of selenocysteine beta-lyase from Citrobacter freundii.

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Purification and characterization of selenocysteine beta-lyase from Citrobacter freundii.