Various functions of selenols and thiols in anaerobic gram-positive, amino acids-utilizing bacteria.
Electron transfer reactions for the reduction of glycine in Eubacterium acidaminophilum involve many selenocysteine (U)- and thiol-containing proteins, as shown by biochemical and molecular analysis. These include an unusual thioredoxin system (-CXXC-), protein A (-CXXU-) and the substrate-specific protein B of glycine reductase (-UXXCXXC-). Most probably a selenoether is formed at protein B by splitting the C-N-bond after binding of the substrate. The carboxymethyl group is then transferred to the selenocysteine of protein A containing a conserved motif. The latter protein acts as a carbon and electron donor by giving rise to a protein C-bound acetyl-thioester and a mixed selenide-sulfide bond at protein A that will be reduced by the thioredoxin system. The dithiothreitol-dependent D-proline reductase of Clostridium sticklandii exhibits many similarities to protein B of glycine reductase including the motif containing selenocysteine. In both cases proprotein processing at a cysteine residue gives rise to a blocked N-terminus, most probably a pyruvoyl group. Formate dehydrogenase and some other proteins from E. acidaminophilum contain selenocysteine, e.g., a 22 kDa protein showing an extensive homology to peroxiredoxins involved in the detoxification of peroxides.
Andreesen
J R
JR
Institut für Mikrobiologie, Martin-Luther Universität Halle-Wittenberg, Germany. j.andreesen@mikrobiologie.uni-halle.de
Wagner
M
M
Sonntag
D
D
Kohlstock
M
M
Harms
C
C
Gursinsky
T
T
Jäger
J
J
Parther
T
T
Kabisch
U
U
Gräntzdörffer
A
A
Pich
A
A
Söhling
B
B
D000596:Amino Acids / Q000378:metabolism*; D001421:Bacteria, Anaerobic / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D006094:Gram-Positive Bacteria / Q000378:metabolism*; D016566:Organoselenium Compounds / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D012643:Selenium / Q000378:metabolism*; D017279:Selenocysteine / Q000378:metabolism; D051140:Selenoproteins; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D013879:Thioredoxins / Q000378:metabolism
D000596:Amino Acids; D001426:Bacterial Proteins; D016566:Organoselenium Compounds; D011506:Proteins; D051140:Selenoproteins; D013438:Sulfhydryl Compounds; D017279:Selenocysteine; D013879:Thioredoxins; D010088:Oxidoreductases; D012643:Selenium