title: N-glycosylation controls trafficking, zymogen activation and substrate processing of proprotein convertases PC1/3 and subtilisin kexin isozyme-1.
abstract: The limited proteolysis of proteins by the proprotein convertases (PCs) is a common means of producing bioactive proteins or peptides. The PCs are associated with numerous human pathologies and their activity can be reduced through the use of specific inhibitors. Here, we demonstrate an alternative approach to inhibiting PCs by altering their N-glycosylation. Through site-directed mutagenesis, we show that the convertase PC1/3 contains two N-glycans, only one of which is critical for its prosegment cleavage. The exact structure of PC1/3 N-glycans does not significantly affect its zymogen activation within endocrine cells, but glycosylation of Asn(146) is critical. Processing of the PC1/3's substrate proopiomelanocortin (POMC) was used in a cell-based assay to screen a collection of 45 compounds structurally related to known glycosidase inhibitors. Two 5-thiomannose-containing disaccharide derivatives were discovered to block PC1/3 and POMC processing into the analgesic peptide β-endorphin. These compounds also reduced the zymogen activation of the convertase subtilisin kexin isozyme-1 (SKI-1), blocked the processing of its substrate the sterol regulatory element-binding protein SREBP-2 and altered its glycosylation. Thus, modification of PC glycosylation may also be a means of blocking their activity, an effect which, in the case of SKI-1, may be of possible therapeutic use since SREBP-2 regulates sterol levels including cholesterol biosynthesis and its metabolism.
authors.affiliation: Department of Chemistry, Simon Fraser University, Burnaby, BC, Canada V5A 1S6.
authors.forename: Wesley F
authors.initials: WF
authors.lastname: Zandberg
authors.forename: Suzanne
authors.initials: S
authors.lastname: Benjannet
authors.forename: Josée
authors.initials: J
authors.lastname: Hamelin
authors.forename: B Mario
authors.initials: BM
authors.lastname: Pinto
authors.forename: Nabil G
authors.initials: NG
authors.lastname: Seidah
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism*; D006031:Glycosylation; D057809:HEK293 Cells; D006801:Humans; D011333:Pro-Opiomelanocortin / Q000378:metabolism; D045664:Proprotein Convertase 1 / Q000378:metabolism*; D043484:Proprotein Convertases / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000502:physiology; D021381:Protein Transport; D012697:Serine Endopeptidases / Q000378:metabolism*; D051782:Sterol Regulatory Element Binding Protein 2 / Q000378:metabolism; D001615:beta-Endorphin / Q000378:metabolism
chemical_list: D004792:Enzyme Precursors; D051782:Sterol Regulatory Element Binding Protein 2; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin; D043484:Proprotein Convertases; D012697:Serine Endopeptidases; C115575:membrane-bound transcription factor peptidase, site 1; D045664:Proprotein Convertase 1