Influence of effectors of the complex-type-oligosaccharide biosynthesis on the formation of proteokeratan sulfate in bovine cornea.

The structural similarity of the inner core of complex-type prosthetic oligosaccharides of N-asparagine glycoproteins and of the linkage region between the polysaccharide part and the protein chain of cornea proteokeratan sulfate makes their biosynthesis via a common route an attractive hypothesis. To test this, a tissue culture system was established to determine the rate of proteokeratan sulfate biosynthesis in bovine cornea and to measure the influence of several effectors of the dolichol pathway on this rate. Addition of dolichyl phosphate enhanced the formation of proteokeratan sulfate. Tunicamycin, 2-deoxy-D-glucose, bromoconduritol and deoxynojirimycin inhibited this process. Swainsonine probably led to the formation of a keratan sulfate with hybrid structure. The results support that the linkage region of cornea proteokeratan sulfate is synthesized via the assembly of a glucosylated dolichyl pyrophosphoryl oligosaccharide, its transfer to protein and subsequent processing by glycosidases.