Variability in Purified Dysfunctional C 1 - inhibitor Proteins from Patients with Hereditary Angioneurotic Edema

Introduction Cl-inhibitor (CI-INH) proteins from normal persons and members of eight different kindred with dysfunctional Ci-INH proteins associated with hereditary angioneurotic edema (HANE) were compared with respect to their inhibitory activity against purified preparations of Cls, plasma kallikrein, activated forms of Hageman factor, and plasmin. Each dysfunctional Ci-INH protein showed a unique spectrum of inhibitory activity against these enzymes. Although none of the dysfunctional CiINH proteins significantly impaired amidolysis by plasmin, all but one inhibited activated Hageman factor. One purified dysfunctional Ci-INH (Ta) inhibited purified Cli to a normal degree. Another Ci-INH (Za) had almost seven times as much inhibitory activity as normal Ci-INH against activated Hageman factor, but had decreased activity against Cli and no activity against plasmin. Analyses of mixtures of plasmin and Ci-INH proteins in SDS gel electrophoresis revealed variability in the patterns of complex formation and cleavage of dysfunctional proteins after exposure to Cli and plasmin. Some bound to plasmin and were cleaved, even though none significantly impaired the amidolytic activity of plasmin. Two were cleaved by Cli, whereas neither normal or other dysfunctional C1INH were cleaved. Dysfunctional Ci-INH proteins from patients with HANE are thus heterogeneous in their inhibitory properties and there must be different structural requirements for the inhibition of the various plasma enzymes that can be regulated by normal Cl-INH. The data suggest that in addition to common sites of interactions between these proteases and Cl-INH, there are also points of contact that are specific for each protease. Genetic mutations leading to structural changes at some of these sites may have differing effects on the interaction between individual proteases and abnormal ClINH proteins. These alterations may allow these proteins to serve as probes for structural requirements for inhibitory actions of normal Ci-INH. Address reprint requests to Dr. Donaldson, Children's Hospital Medical Center. Received for publication 28 Seplember 1983 and in revised form 17 July 1984. Plasmas from persons with hereditary angioneurotic edema (HANE)' are either markedly deficient in Cl-inhibitor (ClINH) activity, as well as CI-INH antigens (type I), or they contain normal or elevated concentrations of dysfunctional Ci-INH protein (type II). Both types of Ci-INH deficiency are inherited as autosomal dominant traits in kindred with HANE. Plasma from patients with type II HANE do not adequately inhibit Cl, or its Cli subunit, and C4 and C2, both of which are substrates of Cl, were readily inactivated in plasma from patients with type II HANE as well as those with type I (1-3). The abnormal CI-INH proteins in plasma and serum of patients with type II HANE were electrophoretically and functionally heterogeneous (3). At least four structural variants of Cl-INH have been identified within this group of patients (3). Despite the heterogeneity among this group of patients, both the tendency to bouts of HANE, and the biochemical disorder, were inherited as autosomal dominant traits in affected kindred (3). Because of the heterogeneity of these proteins, dysfunctional CI-INH was isolated from plasma of 12 affected individuals from eight different kindred with type II HANE. This report describes the capacity of each of these proteins to inhibit ClI, plasma kallikrein, activated Hageman factor (HFa, or Factor XIIa), Hageman factor fragments (HFf), and plasmin; normal CI-INH can inhibit each ofthese proteases in vitro. The inhibition of purified preparations of each of these enzymes by individual dysfunctional Ci-INH proteins differed from one enzyme to another. In addition, the dysfunctional proteins appeared to have unique patterns of inhibition of each enzyme when compared to one another. This suggests that the sites of contact between inhibitor and enzyme are, in part, different and specific to each protease.