A thermostable dolichol phosphoryl mannose synthase responsible for glycoconjugate synthesis of the hyperthermophilic archaeon Pyrococcus horikoshii.
Dolichol phosphoryl mannose synthase (DPM synthase) is an essential enzyme in the synthesis of N- and O-linked glycoproteins and the glycosylphosphatidyl-inositol anchor. An open reading frame, PH0051, from the hyperthermophilic archaeon Pyrococcus horikoshii encodes a DPM synthase ortholog, PH0051p. A full-length version of PH0051p was produced using an E. coli in vitro translation system and its thermostable activity was confirmed with a DPM synthesis assay, although the in vitro productivity was not sufficient for further characterization. Then, a yeast expression vector coding for the N-terminal catalytic domain of PH0051p was constructed. The N-terminal domain, named DPM(1-237), was successfully expressed, and turned out to be a membrane-bound form in Saccharomyces cerevisiae cells, even without its hydrophobic C-terminal domain. The membrane-bound DPM(1-237) was solubilized with a detergent and purified to homogeneity. The purified DPM(1-237) showed thermostability at up to 75 degrees C and an optimum temperature of 60 degrees C. The truncated mutant DPM(1-237) required Mg(2+) and Mn(2+) ions as cofactors the same as eukaryotic DPM synthases. By site-directed mutagenesis, Asp(89) and Asp(91) located at the most conserved motif, DXD, were confirmed as the catalytic residues, the latter probably bound to a cofactor, Mg(2+). DPM(1-237) was able to utilize both acceptor lipids, dolichol phosphate and the prokaryotic carrier lipid C(55)-undecaprenyl phosphate, with Km values of 1.17 and 0.59 microM, respectively. The DPM synthase PH0051p seems to be a key component of the pathway supplying various lipid-linked phosphate sugars, since P. horikoshii could synthesize glycoproteins as well as the membrane-associated PH0051p in vivo.
Urushibata
Yuji
Y
Biological Information Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8566, Japan.
Ebisu
Shogo
S
Matsui
Ikuo
I
D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000235:genetics / Q000378:metabolism; D020134:Catalytic Domain; D017124:Conserved Sequence; D017931:DNA Primers; D004795:Enzyme Stability; D005822:Genetic Vectors; D006001:Glycoconjugates / Q000096:biosynthesis*; D008364:Mannosyltransferases / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010743:Phospholipids / Q000494:pharmacology; D014176:Protein Biosynthesis; D043902:Pyrococcus horikoshii / Q000201:enzymology* / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D016415:Sequence Alignment; D013816:Thermodynamics
D019843:Archaeal Proteins; D017931:DNA Primers; D006001:Glycoconjugates; D010743:Phospholipids; D008364:Mannosyltransferases; C022755:dolichyl-phosphate beta-D-mannosyltransferase