Inhibition of asparagine-linked glycosylation by incorporation of a threonine analog into nascent peptide chains.

The importance of threonine in the Asn-X-Thr recognition sequence for asparagine-linked glycosylation was tested by examining the effect of a threonine analog, beta-hydroxynorvaline, on co-translational glycosylation in Krebs' II ascites tumor lysates. beta-Hydroxynorvaline inhibited the glycosylation of the alpha subunit of human chorionic gonadotropin and the beta subunit of bovine luteinizing hormone; both proteins contain Asn-X-Thr recognition sites. The effect was prevented by threonine, indicating that beta-hydroxynorvaline acted via its incorporation into protein. These results provide direct evidence for the role of threonine in Asn-X-Thr sites for asparagine-linked glycosylation. The results support the view that this site is sensitive to steric hindrance.