Absence of glycosylation on cyanobacterial phycobilisome linker polypeptides and rhodophytan phycoerythrins.
The 27-, 30-, and 33-kDa rod linker polypeptides and the 75-kDa core linker of phycobilisomes from the cyanobacterium Synechococcus sp. strain PCC 7942 have been reported to be glycoproteins with carbohydrate contents ranging from 3.2 to 18.8% and composed of N-acetylgalactosamine and glucose (H.C. Riethman, T.P. Mawhinney, and L.A. Sherman, J. Bacteriol. 170:2433-2440, 1988). Synechococcus sp. strain PCC 7942 phycobilisomes were purified extensively, and the linker polypeptides were separated from the phycobiliproteins by precipitation in 1 M NaSCN. Upon hydrolysis, the linker fraction yielded 0.037% glucose and 0.015% galactosamine by weight and no other carbohydrate. Phycobilisome polypeptides separated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate were subjected to various glycoprotein-specific staining procedures. Linker polypeptides showed very weak concanavalin A binding and no staining by the Schiff-periodate method or by a much more sensitive periodate oxidation-based method. These results indicated that the linker polypeptides are not glycosylated. An earlier report (T. Fujiwara, J. Biochem. 49:361-367, 1961) contended, on the basis of the isolation of sugar-containing peptic chromopeptides from Porphyra tenera R-phycoerythrin, that this red algal phycobiliprotein is a glycoprotein. Analysis of Gastroclonium coulteri R-phycoerythrin and Porphyridium cruentum B-phycoerythrin revealed only traces of carbohydrate in these two proteins, 0.36 and 0.14%, respectively. Results of glycoprotein staining of gels suggested that the carbohydrate in the R-phycoerythrin preparation is due to a glycoprotein contaminant and that neither red algal phycoerythrin is glycosylated.
Fairchild
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Division of Biochemistry and Molecular Biology, MCB:Stanley/Donner ASU, University of California, Berkeley 94720.
Jones
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Glazer
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D002241:Carbohydrates / Q000032:analysis; D003208:Concanavalin A; D000458:Cyanobacteria; D004591:Electrophoresis, Polyacrylamide Gel; D006023:Glycoproteins / Q000032:analysis; D006031:Glycosylation; D015151:Immunoblotting; D045342:Light-Harvesting Protein Complexes; D045524:Phycobilisomes; D010799:Phycoerythrin / Q000737:chemistry* / Q000302:isolation & purification; D010940:Plant Proteins / Q000737:chemistry*
D002241:Carbohydrates; D006023:Glycoproteins; D045342:Light-Harvesting Protein Complexes; D045524:Phycobilisomes; D010940:Plant Proteins; D010799:Phycoerythrin; D003208:Concanavalin A