This Article Full Text Full Text (PDF) Supplemental Data All Versions of this Article: 149/8/4116    most recent Author Manuscript (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Google Scholar Articles by Lee, S.-N. Articles by Lindberg, I. PubMed PubMed Citation Articles by Lee, S.-N. Articles by Lindberg, I.

7B2 Prevents Unfolding and Aggregation of Prohormone Convertase 2

Department of Biochemistry and Molecular Biology (S.-N.L., I.L.), Louisiana State University Health Sciences Center/Research Institute for Children, New Orleans, Louisiana 70118; and Department of Anatomy and Neurobiology (I.L.), University of Maryland Medical School, Baltimore, Maryland 21201

Address all correspondence and requests for reprints to: Dr. Iris Lindberg, Department of Anatomy and Neurobiology, University of Maryland Medical School, 20 Penn Street, Baltimore, Maryland 21201. E-mail: ilind001{at}umaryland.edu.

Prohormone convertase 2 (PC2) requires interaction with the neuroendocrine protein 7B2 for the production of an activatable zymogen; the mechanism for this effect is unknown. 7B2 could act proactively to generate an activation-competent form of pro-PC2 during synthesis, or block spontaneous generation of activation-incompetent forms. We here demonstrate that addition of exogenous recombinant 7B2 to CHO cells expressing pro-PC2 prevented the unfolding and aggregation of secreted PC2 forms in a dose-dependent manner, as assessed by aggregation assays, activity assays, cross-linking experiments, and sucrose density gradients. Intracellular pro-PC2 was also found to exist in part as higher-order oligomers that were reduced in the presence of coexpressed 7B2. 7B2 addition did not result in the acquisition of enzymatic competence unless added before or very rapidly after pro-PC2 secretion, indicating that an activation-competent structure cannot be maintained in the absence of 7B2. Velocity sedimentation experiments showed that addition of extracellular 7B2 solubilized three different PC2 species from a precipitable aggregate: two activatable pro-PC2 species, the intact zymogen and a zymogen with a partially cleaved propeptide, and an inactive 66-kDa form. Our results suggest that 7B2 possesses chaperone activity that blocks partially unfolded pro-PC2 forms from losing catalytic competence and then aggregating. The loss of the catalytically competent conformer appears to represent the earliest indicator of pro-PC2 unfolding and is followed on a slower time scale by the appearance of aggregates. Because 7B2 expression is not confined to areas expressing pro-PC2, 7B2 may represent a general intracellular and extracellular secretory chaperone.