Comparison of the primary structure of the N-terminal CNBr fragments of human, bovine and porcine plasminogen

Compound-Heterozygous Mutations in the Plasminogen Gene Predispose to the Development of Ligneous Conjunctivitis

Homozygous type I plasminogen deficiency has been identified as a cause of ligneous conjunctivitis. In this study, 5 additional patients with ligneous conjunctivitis are examined. Three unrelated patients (1 boy, 1 elderly woman, and 1 man) had plasminogen antigen levels of less than 0.4, less than 0.4, and 2.4 mg/dL, respectively, but had plasminogen functional residual activity of 17%, 18%, and 17%, respectively. These subjects were compound-heterozygotes for different missense mutations in the plasminogen gene: Lys19 → Glu/Arg513 → His, Lys19 → Glu/Arg216 → His, and Lys19 → Glu/Leu128 → Pro, respectively. The other 2 patients, a 14-year-old boy and his 19-year-old sister, who both presented with a severe course of the disease, exhibited plasminogen antigen and functional activity levels below the detection limit (<0.4 mg/dL and <5%, respectively). These subjects were compound-heterozygotes for a deletion mutation (del Lys212) and a splice site mutation in intron Q (Ex17 + 1del-g) in the plasminogen gene. These findings show that certain compound-heterozygous mutations in the plasminogen gene may be associated with ligneous conjunctivitis. Our findings also suggest that the severity of clinical symptoms of ligneous conjunctivitis and its associated complications may depend on the amount of plasminogen functional residual activity.

Complete amino acid sequence of bovine plasminogen. Comparison with human plasminogen

The amino acid sequence of the single polypeptide chain of bovine plasminogen (786 residues, Mr 88092) was determined. Cleavage with CNBr yielded 13 fragments of which six originated from cleavage sites different from human plasminogen. Digestion with elastase gave three major fragments: kringles (1 + 2 + 3) and kringle 4, both with intact lysine binding sites, and mini-plasminogen. Subfragmentation was achieved mainly with 2-(2-nitrophenylsulfenyl)-3-methyl-3'-bromoindolenine (BNPS-skatole), Staphylococcus aureus V8 protease and trypsin. The sequences of fragments which were determined by automated Edman degradation, were aligned with overlapping sequences, or, in a few instances, by homology with the known sequence of human plasminogen. Sequence comparison with the human protein showed varying degrees of homology in the different functional and structural domains. The overall identity (78%) is practically the same as that found in those regions corresponding to the heavy (79%) and the light chain (80%) of plasmin. The average degree of identity among the kringles is 83%. Outside the kringle structures the extent of identity decreases, to 65% in the N-terminal region and to about 50% in the connecting strands between the kringles except for the strand between kringles 2 and 3, where only one out of 12 residues is exchanged. The results reported show that bovine plasminogen apparently contains the same structural and functional domains as human plasminogen. Bovine plasminogen also contains two carbohydrate moieties. The only partially substituted N-glycosidic site, Asn289, corresponds to partially glycosylated Asn288 in human plasminogen, whereas the O-glycosidic site of the human sequence, Thr345, is shifted to Ser339 in bovine plasminogen.

Group-directed modification of bacteriorhodopsin by arylisothiocyanates. Labeling, identification of the binding site and topology

Group-directed hydrophobic modification of membrane-integrated protein segments by arylisothiocyanates is applied to bacteriorhodopsin. Labeling of purple membrane with phenylisothiocyanate and 4-N,N'-dimethylamino-azobenzene-4'-isothiocyanate results in covalent modification of a unique lysine epsilon-amino group of bacteriorhodopsin. Lysine residue 41, located in the amino-terminal chymotryptic fragment, has been identified as the arylisothiocyanate binding site by established sequencing techniques. The phenylisothiocyanate binding site is not accessible for the aqueously soluble analog p-sulfophenylisothiocyanate. Furthermore, the acid-induced bathochromic shift of the bound chromophore reagent is not observed following acidification of 4-N,N'-dimethylamino-azobenzene-4'-isothiocyanate-labeled purple membrane. The modification thus occurs in the hydrophobic membrane domain, providing further evidence for intramembraneous disposition of the modified protein segment. Light-induced proton translocation is preserved in reconstituted vesicles containing either phenylisothiocyanate-modified or 4-N,N'-dimethylamino-azobenzene-4'-isothiocyanate-modified bacteriorhodopsin.

Primary structure of porcine plasminogen. Isolation and characterization of CNBr-fragments and their alignment within the polypeptide chain

The single polypeptide chain of native plasminogen (molecular weight approx. 90000) after CNBr-cleavage and gel filtration (Sephadex G-75) yielded a high molecular weight core fraction of fragments linked by disulfide bridges and three fragments of lower molecular weight (N-terminal and C-terminal CNBr-fragments and dodecapeptide). From the reduced and S-carboxamidomethylated core fraction an additional seven fragments with molecular weights between 2000 and 38000 were obtained. The CNBr-fragments were aligned in the porcine plasminogen polypeptide chain according to sequence homologies with the known primary structure of human plasminogen. Due to the lack of two methionine residues in kringle 1 and in the N-terminal part of the light chain region and to an additional methionine residue in kringle 2 the CNBr-fragment pattern differs from that of human plasminogen. Affinity chromatography of elastase-digested, native plasminogen yielded three fragments with intact lysine binding sites, originating from the heavy chain region and a non-adsorbable fragment, corresponding to human 'mini'-plasminogen. This fragment was converted to urokinase into a proteolytically active protein which served for the isolation of the porcine plasmin light chain. With the aid of the fragments produced by the CNBr and elastase cleavage approx. 350 residues were sequenced, of which about 80% showed identity with the sequence of human plasminogen. This percentage varied depending on the region of the molecule, with the highest extent of identity (80--90%) found in the analyzed kringles 2 and 4.