POSTTRANSLATIONAL N-GLYCOSYLATION OF A TRUNCATED FORM OF A PEPTIDE PROCESSING ENZYME

Peptidylglycine alpha-amidating monooxygenase (PAM) catalyzes the carb oxyl-terminal amidation of bioactive peptides through a two-step react ion involving the monooxygenase and lyase domains. PAM undergoes endop roteolytic cleavage in neuroendocrine cells in the lyase domain. To de termine which of the two possible paired basic sites is utilized, trun cated PAM proteins ending at these sites were stably expressed in Chin ese hamster ovary cells. While characterizing the truncation mutants, it became apparent that N-glycosylation occurred post-translationally at the single site localized near the carboxyl terminus of the lyase d omain. The post-translational N-glycosylation of this site does not re quire the newly synthesized protein to remain tightly bound to membran es. Both malfolded, secretion incompetent proteins and fully active, s ecreted proteins were subject to post-translational N-glycosylation.