9.B.115 The Steroid 5α-reductase/Lamin B Receptor (LBR) Family
The proteins of the DUF1295 Superfamily, present in bacteria and eukaryotes, appear to be of unknown function. However, several entries in NCBI are annotated as various enzymes. The most common annotation names several of these homologues as steroid 5α-reductases. These homologs are integral membrane proteins, most with 8 - 10 TMSs.
The lamin B receptor of fruit flies anchors the lamina and the heterochromatin to the inner nuclear membrane. It has the following properties in
common with the vertebrate LBR. First, structural predictions indicate
that the 741 amino acid dLBR protein possesses a highly charged
N-terminal domain of 307 amino acids followed by eight (to ten) transmembrane
segments in the C-terminal domain of the molecule. Second, the dLBR is an
integral membrane protein of the inner nuclear membrane. Third, dLBR binds
to the Drosophila B-type lamin Dm0. Fourth, the N-terminal domain is sufficient for in vitro binding to sperm chromatin and lamin
Dm0. In contrast to the human LBR, dLBR does not possess sterol C14
reductase activity when it is expressed in the Saccharomyces cerevisiae erg24 mutant, which lacks sterol C14 reductase activity. Thus, during evolution, the enzymatic activity of this
insect protein had been lost. Deletion gave rise to no obvious effect
on the nuclear architecture or viability of treated cells and embryos,
whereas the depletion of Drosophila lamin Dm0 in cultured cells and
embryos caused morphological alterations of nuclei, nuclear fragility
and the arrest of embryonic development. (Wagner et al. 2004). One such homolog is found under TC# 1.I.1.1.5 as part of the nuclear pore complex.
Oxidoreductase of 240 aas and 7 TMSs.
Rhodophyta
Oxidoreductase of Galdieria sulphuraria (M2X3K0)
DUF1295 domain-containing protein of 249 aas and 6 TMSs in a 2 + 2 + 2 TMS arrangement.
DUF1295 protein of Rhizobium mesoamericanum
Isoprenylcysteine carboxylmethyltransferase family protein of 158 aas and 4 TMSs in a 2 + 2 TMS arrangement.
Carboxylmethyltransferase of Nitratireductor soli
Bifunctional phosphatidyl-N-methylethanolamine N-methyltransferase/phosphatidyl-N-dimethylethanolamine N-methyltransferaseof 206 as and 3 or 4 TM
Methyl transferase of Saccharomyces cerevisiae
Uncharacterized protein of 848 aas and 14 TMSs.
UP of Kazachstania naganishii
Uncharacterized protein of 569 aas and 9 or 10 TMSs
UP of Asanoa ishikariensis
Membrane protein of 288 aas and 8 TMSs in a 2+2+2+2 arrangement.
Actinobacteria
Membrane protein of Arthrobacter phenanthrenivorans (F0M2Z7)
SαR homologue of 295 aas and 8 putative TMSs
Actinobacteria
SαR homologue of Mycobacterium marinum (B2HS04)
SαR homologue of 321 aas and 6 TMSs
Plants
SαR homologue of Chlamydomonas reinhardtii (A8ILY4)
SαR homologue of 300 aas and 5 putative TMSs
Stramenopiles (Marine diatoms)
SαR homologue of Thalassiosira pseudonana (B8C953)
Uncharacterized protein of 243 aas and 5 TMSs; possible isoprenylcysteine carboxyl methyltransferase family protein
Bacteroideetes
UP of Sphingobacterium spiritivorum
Uncharacterized protein of 229 aas and 5 or 6 TMSs.
UP of Candidatus Thorarchaeota archaeon AB_25 (marine sediment metagenome)
Uncharacterized protein of 207 aas and 4 TMSs.
UP of Candidatus Thorarchaeota archaeon AB_25 (marine sediment metagenome)
Uncharacterized protein of 203 aas and 4 TMSs in a 1 + 2 + 1 TMS arrangement.
UP of Candidatus Thorarchaeota archaeon AB_25 (marine sediment metagenome)
Phosphatidyl-N-methylethanolamine N-methyltransferase of 168 aas and 3 or 4 TMSs.
Methyltransferase of Sorghum bicolor
Uncharacterized protein of 197 aas and 6 TMSs
UP of Sphaeroforma arctica
Uncharacterized protein of 180 aas and 4 or 5 TMSs
UP of Chlorella variabilis
Uncharacterized protein of 182 aas and 6 putative TMSs.
UP of Acidithiobacillus thiooxidans
The lamin B receptor , LBR, of 741 aas and 8 - 10 TMSs. See family description for details.
LBR of Drosophila melanogaster (Fruit fly)
Delta24(24(1))-sterol reductase (SR) of 489 aas and 9 TMSs in a 4 + 4 + 1 TMS arrangement.
SR of Cryptococcus neoformans
Uncharacterized protein of 349 aas and 8 or 9 TMSs in a 3 + 2 + 1 + 2 or 3 TMS arrangement.
UP of Cannabis sativa
FACT complex subunit spt16-like of 1494 aas and 11 or 12 TMSs in a 4 + 4 + 2 or 3 +1 TMS arrangement.
Spt16 homolog of Quercus suber
7-Dehydrocholesterol reductase-like isoform X1 of 573 aas and 9 or 10 TMSs in a 4 + 4 + 1 or 2 TMS arrangement.
7-DCR of Durio zibethinus
DUF1295 domain-containing protein of 379 aas and 9 - 10 TMSs in a 3 + 4 + 2 or 3 TMS arrangement.
DUF1295 protein of Nitrospinae bacterium
7-Dehydrocholesterol reductase of 422 aas and 9 or 10 TMSs in a 4 (2 + 2) + 4 (2 + 2) + 1 or 2 TMS arrangement.
7-DCR of Deltaproteobacteria bacterium