title: Homologous substitution of ACE C-domain regions with N-domain sequences: effect on processing, shedding, and catalytic properties.
abstract: Angiotensin-converting enzyme (ACE) exists as two isoforms: somatic ACE (sACE), comprised of two homologous N and C domains, and testis ACE (tACE), comprised of the C domain only. The N and C domains are both active, but show differences in substrate and inhibitor specificity. While both isoforms are shed from the cell surface via a sheddase-mediated cleavage, tACE is shed much more efficiently than sACE. To delineate the regions of tACE that are important in catalytic activity, intracellular processing, and regulated ectodomain shedding, regions of the tACE sequence were replaced with the corresponding N-domain sequence. The resultant chimeras C1-163Ndom-ACE, C417-579Ndom-ACE, and C583-623Ndom-ACE were processed to the cell surface of transfected Chinese hamster ovary (CHO) cells, and were cleaved at the identical site as that of tACE. They also showed acquisition of N-domain-like catalytic properties. Homology modelling of the chimeric proteins revealed structural changes in regions required for tACE-specific catalytic activity. In contrast, C164-416Ndom-ACE and C191-214Ndom-ACE demonstrated defective intracellular processing and were neither enzymatically active nor shed. Therefore, critical elements within region D164-V416 and more specifically I191-T214 are required for the processing, cell-surface targeting, and enzyme activity of tACE, and cannot be substituted for by the homologous N-domain sequence.
authors.affiliation: Division of Medical Biochemistry and Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town 7925, South Africa.
authors.forename: Zenda L
authors.initials: ZL
authors.lastname: Woodman
authors.forename: Sylva L U
authors.initials: SL
authors.lastname: Schwager
authors.forename: Pierre
authors.initials: P
authors.lastname: Redelinghuys
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Chubb
authors.forename: Elizabeth L
authors.initials: EL
authors.lastname: van der Merwe
authors.forename: Mario R W
authors.initials: MR
authors.lastname: Ehlers
authors.forename: Edward D
authors.initials: ED
authors.lastname: Sturrock
mesh_terms: D000818:Animals; D016466:CHO Cells; D002384:Catalysis; D020134:Catalytic Domain; D006224:Cricetinae; D004789:Enzyme Activation / Q000502:physiology; D007527:Isoenzymes / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008297:Male; D007703:Peptidyl-Dipeptidase A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013737:Testis / Q000201:enzymology
chemical_list: D007527:Isoenzymes; D011993:Recombinant Fusion Proteins; D007703:Peptidyl-Dipeptidase A