PROBING EPITOPES ON HUMAN PRORENIN DURING ITS PROTEOLYTIC AND NONPROTEOLYTIC ACTIVATION

The conformational changes of prorenin (PR) that are associated with i ts reversible non-proteolytic activation and irreversible proteolytic activation were monitored with immunoradiometric assays, using antibod ies against epitopes belonging to the propeptide or the renin part of PR. Binding of PR to the renin inhibitor remikiren or protonation of P R resulted in the slowly progressive and simultaneous expression (t(1/ 2) congruent to 3.5-5.0 h at 4 degrees C) of epitopes of the N-termina l and C-terminal halves of the propeptide and an epitope that is manif est on renin but not on native non-activated PR. During reversible PR activation-inactivation, expression and disappearance of these epitope s coincided with the appearance and disappearance of enzyme activity. Cleavage of the propeptide from the renin part of PR by plasmin, as de monstrated by the failure of remikiren to unmask the N-terminal and C- terminal propeptide epitopes, was, with some time lag, followed by the simultaneous expression (t(1/2) congruent to 60 min at 4 degrees C) o f the renin-specific epitope and enzymatic activity. Based on these fi ndings we propose a model for the non-proteolytic activation of PR tha t involves the formation of an intermediary form of activated PR with the following properties: (1) the covalently bound propeptide has move d out of the active-site cleft, so that binding sites are exposed to a ctive site ligands, (2) the propeptide is still not in the 'relaxed' c onformation that is characteristic for fully, non-proteolytically, act ivated PR, and (3) the N-terminal part of the renin polypeptide chain has not yet attained the proper location that is required for enzymati c activity. (C) 1998 Elsevier Science B.V. All rights reserved.