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Related Concept Videos

Complement System01:27

Complement System

The complement system is a group of approximately 20 plasma proteins that strengthen the body's defenses against infections through opsonization, inflammation, and cell lysis. Opsonization involves coating pathogens with complement proteins, making them more recognizable and facilitating phagocyte engulfment. Certain complement proteins induce inflammation that attracts immune cells to the site of infection. Cell lysis involves the destruction of pathogens through the formation of a membrane...
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After a fibrin clot is formed, the next step is clot retraction, a vital process facilitated by platelet contractile proteins, such as actin and myosin. These proteins pull the fibrin strands closer together and condense the clot. This action reduces the size of the clot, creating a smaller, denser structure that effectively seals off the damaged vessel. Clot retraction consolidates the clot and helps with wound healing by bringing the edges of the damaged blood vessel closer together.
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Hemostasis is a crucial process that prevents excessive blood loss from damaged blood vessels. It involves various mechanisms such as vasoconstriction, platelet adhesion and activation, and fibrin formation. The importance of each mechanism depends on the type of vessel injury. In contrast, thrombosis is the abnormal formation of a blood clot within the blood vessels, leading to potential complications if the clot obstructs blood flow. Thrombosis can be caused by increased coagulability of the...
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Plakins are large proteins with binding domains for microtubules, microfilaments, intermediate filaments, and membrane-associated protein complexes at cell junctions. Plakin functions are evolutionarily conserved and are primarily involved in organizing the different components of the cytoskeleton by crosslinking them to each other and connecting them to the cell-matrix and cell adhesion complexes. They are also known to interact with signal transducers, serve as scaffolds for signaling...
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Antimicrobial proteins are important components of the immune system. They aid the body in combating pathogens by either killing them directly or hindering their replication processes. Four main types of antimicrobial substances are interferons, the complement system, iron-binding proteins, and antimicrobial proteins.
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Plasminogen is a complement inhibitor.

Diana Barthel1, Susann Schindler, Peter F Zipfel

  • 1Department of Infection Biology, Leibniz Institute for Natural Product Research and Infection Biology, Jena, Germany.

The Journal of Biological Chemistry
|March 28, 2012
PubMed
Summary
This summary is machine-generated.

Plasminogen, a protein involved in blood clot dissolution, also regulates the complement system. It inhibits complement activation and degrades complement proteins, impacting immune evasion by pathogens.

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Area of Science:

  • Biochemistry
  • Immunology
  • Molecular Biology

Background:

  • Plasminogen is a plasma glycoprotein converted to plasmin, which dissolves fibrin clots and extracellular matrix.
  • The complement cascade is a critical part of the innate immune system, involving a series of protein activations.

Purpose of the Study:

  • To investigate the role of plasminogen and its active form, plasmin, in the complement cascade.
  • To elucidate the interactions between plasminogen/plasmin and complement proteins like C3, C3b, C3d, and C5.

Main Methods:

  • Investigated plasminogen binding to complement proteins (C3, C3b, C3d, C5) using biochemical assays.
  • Assessed the effect of plasminogen on Factor I-mediated C3b degradation.
  • Utilized hemolytic assays to evaluate plasmin's inhibition of complement activation via alternative and classical pathways.
  • Analyzed complement protein cleavage fragments generated by plasmin.

Main Results:

  • Plasminogen binds to C3, C3b, C3d, and C5 via lysine residues in an ionic strength-dependent manner.
  • Plasminogen enhances Factor I-mediated C3b degradation in the presence of Factor H.
  • Plasmin inhibits complement activation and cleaves C3b and C5 into distinct fragments, suggesting loss of effector function.

Conclusions:

  • Plasminogen/plasmin acts as a regulator of the complement cascade, influencing both complement activation and degradation.
  • The interaction between plasminogen and complement provides a mechanism for immune evasion by pathogens.
  • Plasminogen/plasmin bridges the complement and coagulation systems, highlighting its central role in vertebrate physiology.