Dissociation of the complex between the neuroendocrine chaperone 7B2 and prohormone convertase PC2 is not associated with proPC2 maturation.
7B2 is a highly conserved neuroendocrine protein that is associated with the proform of the prohormone convertase PC2 in the early stages of the secretory pathway in intermediate pituitary cells of Xenopus laevis. Subsequent processing of 7B2 and dissociation of the 7B2/proPC2 complex is thought to be associated with the conversion of proPC2 to the mature enzyme. Here, we report that, in both Xenopus and mouse intermediate cells, proPC2 maturation does not take place when the proenzyme is associated with the 7B2 precursor and that, in contrast to the previous notion, dissociation of the complex between proPC2 and the N-terminal 7B2 fragment precedes, and is thus not directly linked to, proPC2 maturation. In vitro, conversion of newly synthesized proPC2 was efficiently blocked by recombinant 7B2 and studies with truncation mutants indicated that a short segment in the C-terminal region of 7B2 is necessary and sufficient for this inhibitory effect. Our results indicate that, after 7B2 precursor processing and dissociation of the N-terminal fragment, the C-terminal fragment of 7B2 may remain associated with proPC2, thereby preventing autocatalytic conversion of the proenzyme until the appropriate site for activation in the secretory pathway is reached.
Braks
J A
JA
Department of Animal Physiology, University of Nijmegen, The Netherlands.
Van Horssen
A M
AM
Martens
G J
GJ
D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000032:analysis / Q000096:biosynthesis; D020126:Brefeldin A; D003517:Cyclopentanes / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004792:Enzyme Precursors / Q000378:metabolism; D051379:Mice; D008815:Mice, Inbred Strains; D018832:Molecular Chaperones / Q000378:metabolism*; D008985:Monensin / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D051859:Neuroendocrine Secretory Protein 7B2; D010902:Pituitary Gland / Q000378:metabolism*; D010907:Pituitary Hormones / Q000378:metabolism*; D011233:Precipitin Tests; D011333:Pro-Opiomelanocortin / Q000096:biosynthesis; D045706:Proprotein Convertase 2; D043484:Proprotein Convertases; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000378:metabolism; D013381:Subtilisins / Q000378:metabolism*; D014982:Xenopus laevis
D003517:Cyclopentanes; D004792:Enzyme Precursors; D018832:Molecular Chaperones; D009419:Nerve Tissue Proteins; D051859:Neuroendocrine Secretory Protein 7B2; D010907:Pituitary Hormones; D011994:Recombinant Proteins; D020126:Brefeldin A; D011333:Pro-Opiomelanocortin; D008985:Monensin; D043484:Proprotein Convertases; D013381:Subtilisins; D045706:Proprotein Convertase 2; D016282:Aspartic Acid Endopeptidases