A new Dol-P-Man:protein O-D-mannosyltransferase activity from Saccharomyces cerevisiae.
The deletion of the protein mannosyltransferase 1 gene (PMT1) of Saccharomyces cerevisiae results in viable cells. O-Mannosylation of proteins is reduced to about half of the value in comparison to wild-type cells. In order to distinguish between the the PMT1 gene product (= Pmt1p) and residual transferase activity, an in vitro assay to measure Dol-P-Man:protein mannosyltransferase activity in cells deleted for PMT1 has been developed. The transferase activity of these cells exhibits a pH optimum of 6.5 as compared to pH 7.5 for Pmt1p. The Km value of the residual enzyme activity for the hexapeptide YNPTSV is 7 times higher than that of Pmt1p and shows a clear preference for the seryl residue. Differences in substrate affinities as well as in seryl/threonyl depend on the specific sequence of the peptides used in the enzyme assay. The new enzyme activity shows a significantly lower thermal stability as compared to Pmt1p.
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Lehrstuhl für Zellbiologie und Pflanzenphysiologie, Universität Regensburg, FRG.
Strahl-Bolsinger
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Tanner
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D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000201:enzymology; D017353:Gene Deletion; D005800:Genes, Fungal; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D008364:Mannosyltransferases / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D013379:Substrate Specificity; D013816:Thermodynamics
D007527:Isoenzymes; D008364:Mannosyltransferases; C082696:protein O-mannosyltransferase