Glycoprotein biosynthesis in Chlamydomonas. A mannolipid intermediate with the properties of a short-chain alpha-saturated polyprenyl monophosphate.
A crude membrane preparation of the unicellular green alga Chlamydomonas reinhardii was found to catalyse the incorporation of D-[14C]mannose from GDP-D-[14C]-mannose into a chloroform/methanol-soluble compound and into a trichloroacetic acid-insoluble polymer fraction. The labelled lipid revealed the chemical and chromatographic properties of a short-chain (about C55-C65) alpha-saturated polyprenyl mannosyl monophosphate. In the presence of detergent both long-chain (C85-C105) dolichol phosphate and alpha-unsaturated undecaprenyl phosphate (C55) were found to be effective as exogenous acceptors of D-mannose from GDP-D-[14C]mannose to yield their corresponding labelled polyprenyl mannosyl phosphates. Exogenous dolichyl phosphate stimulated the incorporation of mannose from GDP-D-[14C]mannose into the polymer fraction 5-7-fold, whereas the mannose moiety from undecaprenyl mannosyl phosphate was not further transferred. Authentic dolichyl phosphate [3H]mannose and partially purified mannolipid formed from GDP-[14C]mannose and exogenous dolichyl phosphate were found to function as direct mannosyl donors for the synthesis of labelled mannoproteins. These results clearly indicate the existence of dolichol-type glycolipids and their role as intermediates in transglycosylation reactions of this algal system. Both the saturation of the alpha-isoprene unit and the length of the polyprenyl chain may be regarded as evolutionary markers.
D002696:Chlamydomonas / Q000378:metabolism*; D002848:Chromatography, DEAE-Cellulose; D002850:Chromatography, Gel; D002855:Chromatography, Thin Layer; D004287:Dolichol Monophosphate Mannose / Q000096:biosynthesis*; D004288:Dolichol Phosphates / Q000378:metabolism; D006023:Glycoproteins / Q000096:biosynthesis*; D006868:Hydrolysis; D008358:Mannose / Q000378:metabolism; D008562:Membrane Glycoproteins; D011105:Polyisoprenyl Phosphate Sugars / Q000096:biosynthesis*; D011106:Polyisoprenyl Phosphates / Q000378:metabolism
D004288:Dolichol Phosphates; D006023:Glycoproteins; D008562:Membrane Glycoproteins; D011105:Polyisoprenyl Phosphate Sugars; D011106:Polyisoprenyl Phosphates; C025363:mannoproteins; C028306:dolichol monophosphate; C009621:undecaprenyl phosphate; D004287:Dolichol Monophosphate Mannose; D008358:Mannose