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Converting tissue-type plasminogen activator into a zymogen

K Tachias1, E L Madison

  • 1Department of Vascular Biology, Scripps Research Institute, La Jolla, California 92037, USA.

The Journal of Biological Chemistry
|November 15, 1996
PubMed
Summary
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Tissue-type plasminogen activator (t-PA) shows low zymogenicity compared to urokinase (u-PA). A key acidic residue at position 144 dictates this functional difference between these related serine proteases.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Enzymology

Background:

  • Tissue-type plasminogen activator (t-PA) and urokinase (u-PA) are related serine proteases involved in fibrinolysis.
  • Unlike most serine proteases, t-PA is not a true zymogen, exhibiting low zymogenicity (5-10).
  • The molecular basis for the distinct zymogenic properties of t-PA and u-PA remains unclear.

Purpose of the Study:

  • To investigate the molecular basis for the differing zymogenicities of t-PA and u-PA.
  • To identify the key structural determinant responsible for the functional distinction between t-PA and u-PA.

Main Methods:

  • Analysis of protease domain structures of two-chain t-PA and u-PA.
  • Molecular modeling of single-chain t-PA and u-PA.
  • Site-directed mutagenesis of t-PA at position 144.

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Main Results:

  • The presence or absence of an acidic residue at position 144 (chymotrypsin numbering) is proposed as the primary determinant of zymogenicity.
  • Mutation of t-PA's histidine 144 to an acidic residue (like in u-PA) significantly enhanced its zymogenicity.
  • A t-PA variant with aspartate at position 144 showed a zymogenicity of 150, compared to wild-type t-PA (9) and u-PA (250).

Conclusions:

  • An acidic residue at position 144 is critical for the low zymogenicity of t-PA.
  • This residue selectively suppresses the activity of single-chain t-PA, thereby increasing its zymogenicity.
  • The findings elucidate a key structural difference underlying the distinct activation mechanisms of t-PA and u-PA.