Biochemical properties of recombinant mutants of nonglycosylated single chain urokinase-type plasminogen activator.
The role of glycosylation on the enzymatic properties of single chain urokinase-type plasminogen activator (scu-PA) was investigated by site-specific mutagenesis of the glycosylated Asn-302 residu to Gln. In addition, the role of the NH2-terminal polypeptide chain and of the Cys-148 to Cys-279 interchain disulphide bond on the activity of non-glycosylated scu-PA was investigated. Therefore, variants of recombinant scu-PA (rscu-PA) were produced by transfecting Chinese hamster ovary cells with cDNA encoding rscu-PA N302Q (rscu-PA with Asn-302 to Gln mutation), rscu-PA C279A,N302Q (rscu-PA with Cys-279 to Ala and Asn-302 to Gln mutations) or rscu-PA del(N2-F157)C279A,N302Q (rscu-PA C279A,N302Q with deletion of Asn-2 through Phe-157). These mutants were purified to homogeneity from conditioned cell culture medium and were obtained essentially as single chain molecules with specific activities on fibrin plates of (mean +/- S.E.; n = 6) 45,000 +/- 5000. IU/mg, 19,000 +/- 800 IU/mg and < or = 100 IU/mg for rscu-PA N302Q, rscu-PA C279A,N302Q and rscu-PA del(N2-F157)C279A,N302Q, respectively, as compared to 64,000 +/- 2600 IU/mg for wild-type rscu-PA obtained in the same expression system. Plasmin quantitatively converts rscu-PA N302Q and rscu-PA C279A,N302Q to amidolytically active two-chain derivatives with a specific activity of 56,000 IU/mg and 32,000 IU/mg, respectively, as compared to 75,000 IU/mg for wild-type rscu-PA. Plasminogen activation as a function of time was comparable for rscu-PA N302Q and wild-type rscu-PA, and somewhat slower for rscu-PA C279A,N302Q. In a human plasma milieu in vitro, consisting of a 125I-fibrin labeled plasma clot submerged in plasma, 50 percent clot lysis in 2 h required 2.2 micrograms/ml rscu-PA N302Q and 6.0 micrograms/ml rscu-PA C279A,N302Q, as compared to 3.2 micrograms/ml wild-type rscu-PA. In contrast, rscu-PA del(N2-F157)C279A,N302Q was not converted to an amidolytically active two chain derivative by plasmin, and did not induce significant plasminogen activation in purified systems or clot lysis in a human plasma milieu. Following bolus injections in hamsters, the initial half-lives (1.8-2.6 min) and the plasma clearances (0.6-1.5 ml min-1) were comparable for wild-type rscu-PA and for the three rscu-PA mutants. These results suggest that the fibrinolytic activity in a plasma milieu in vitro and the in vivo turnover of rscu-PA are not markedly affected by the absence of carbohydrate.(ABSTRACT TRUNCATED AT 400 WORDS)
Li
X K
XK
Center for Thrombosis and Vascular Research, University of Leuven, Belgium.
Lijnen
H R
HR
Nelles
L
L
Hu
M H
MH
Collen
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D000818:Animals; D001483:Base Sequence; D006224:Cricetinae; D004789:Enzyme Activation; D005341:Fibrinolysin / Q000494:pharmacology; D005342:Fibrinolysis; D006031:Glycosylation; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D010958:Plasminogen / Q000378:metabolism; D011994:Recombinant Proteins; D013329:Structure-Activity Relationship; D014568:Urokinase-Type Plasminogen Activator / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics
D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins; D010958:Plasminogen; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator