Bovine DNase I contains two potential N-linked glycosylation sites with the sequences Asn18-Ala-Thr and Asn106-Asp-Ser. A previous report established that pancreatic DNase I has only one sugar chain at Asn18 [Liao, Salnikow, Moore and Stein (1973) J. Biol. Chem. 248, 1489–1495]. We found, however, that bovine DNase I expressed in COS-1 cells was glycosylated about 70% at Asn106 in addition to being completely glycosylated at Asn18. Glycosylation of Asn106 increased to 97% when Asp107 was mutated to Glu or when Ser108 was mutated to Thr. Mutation of Asp107 to Trp had no effect, whereas a substitution with Pro at this position abolished glycosylation of Asn106. Analysis of the state of glycosylation of DNase I purified from a variety of bovine tissues revealed that DNase I from spleen, submaxillary gland, lung and adrenal had two sugar chains, whereas enzyme from pancreas and kidney had only one sugar chain. These findings demonstrate a major difference in the ability of various tissues to utilize N-linked glycosylation signals that contain suboptimal residues in the second and third positions.

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