Taskov K et al. (2005) Nucleic Acids Res "Nematode selenoproteome: the use of the selenocysteine insertion system to decode one codon in an animal genome?"

Castellano S, Taskov K, Lobanov AV, Kryukov GV, Chapple C, Korotkov KV, Guigo R, Gladyshev VN

[Nucleic Acids Res, 2005]

Selenocysteine (Sec) is co-translationally inserted into selenoproteins in response to codon UGA with the help of the selenocysteine insertion sequence (SECIS) element. The number of selenoproteins in animals varies, with humans having 25 and mice having 24 selenoproteins. To date, however, only one selenoprotein, thioredoxin reductase, has been detected in Caenorhabditis elegans, and this enzyme contains only one Sec. Here, we characterize the selenoproteomes of C.elegans and Caenorhabditis briggsae with three independent algorithms, one searching for pairs of homologous nematode SECIS elements, another searching for Cys- or Sec-containing homologs of potential nematode selenoprotein genes and the third identifying Sec-containing homologs of annotated nematode proteins. These methods suggest that thioredoxin reductase is the only Sec-containing protein in the C.elegans and C.briggsae genomes. In contrast, we identified additional selenoproteins in other nematodes. Assuming that Sec insertion mechanisms are conserved between nematodes and other eukaryotes, the data suggest that nematode selenoproteomes were reduced during evolution, and that in an extreme reduction case Sec insertion systems probably decode only a single UGA codon in C.elegans and C.briggsae genomes. In addition, all detected genes had a rare form of SECIS element containing a guanosine in place of a conserved adenosine present in most other SECIS structures, suggesting that in organisms with small selenoproteomes SECIS elements may change rapidly.

ccnk

CyCliN K

KR1234

Caenorhabditis elegans

kcc

K+/Cl- Cotransporter

gamma-glutamyl carboxylase activity

Catalysis of the reaction: peptidyl-glutamate + reduced vitamin K + CO2 + O2 = peptidyl-gamma-carboxyglutamate + vitamin K epoxide.

kcmf

K (potassium) Channel Modulatory Factor

nkcc

Na-K-Cl Cotransporter homolog

Kocuria rosea ATCC 186 : pgp-5

"Other K. rhizophila isolates or the closely related K. kristinae and K. marina also abrogated induction of pgp-5::gfp in the germline translation mutant animals, but feeding on other close taxons, K. rosea or Micrococcus luteus, did not disrupt pgp-5 induction (Fig. 6b)."

nkb

Na+/K+ ATPase, Beta subunit

nka

Na/K ATPase, Alpha subunit