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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...
Extrinsic and Intrinsic Pathways of Hemostasis01:20

Extrinsic and Intrinsic Pathways of Hemostasis

Blood clotting or coagulation involves extrinsic and intrinsic pathways, which ultimately merge into the common pathway, forming a fibrin clot.
The Extrinsic Pathway
The extrinsic pathway of coagulation is typically initiated by tissue damage that exposes blood to tissue factor (TF), a protein released by the damaged tissue cells outside the blood vessels—this interaction with TF triggers biochemical reactions involving specific clotting factors. The key player here is Factor VII, which forms a...
Caspases01:24

Caspases

Caspase, a family of cysteine proteases, serve as effectors in apoptosis. The ced3 gene in C.elegans was first identified to be involved in apoptosis. This gene encodes the ced-3 caspase that is similar to the interleukin-1-beta converting enzyme or ICE in mammals. In addition to apoptosis, caspases also function in the inflammatory response. Inflammatory caspases are essential in activating pro-inflammatory cytokines that recruit immune cells and block the replication of pathogens inside cells.
Antimicrobial Proteins01:23

Antimicrobial Proteins

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.
Interferons
Interferons (IFNs) are proteins produced by lymphocytes, macrophages, and fibroblasts infected with viruses. While IFNs cannot prevent viruses from entering and...
Antibody Actions01:26

Antibody Actions

Antibodies, or immunoglobulins, are critical players in the immune system's arsenal against invading pathogens. Produced by B cells and plasma cells, their primary role is to detect and bind to specific antigens, molecules found on the surface of pathogens like bacteria or viruses. Beyond antigen recognition, antibodies perform several vital functions that contribute to immune defense.
Neutralization
Antibodies can bind to pathogens, preventing them from infecting host cells. This process...
Formation of Lipopolysaccharides01:19

Formation of Lipopolysaccharides

Lipopolysaccharides (LPS) are crucial components of the outer membrane of Gram-negative bacteria, serving both structural and functional roles. It contributes to membrane stability and protects bacteria from host immune responses. LPS is composed of three major regions—lipid A, a core oligosaccharide, and an O antigen. The biosynthesis and assembly of LPS involve a highly coordinated set of enzymatic reactions and transport mechanisms. Additionally, LPS is recognized as an endotoxin, triggering...

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High-resolution Melting PCR for Complement Receptor 1 Length Polymorphism Genotyping: An Innovative Tool for Alzheimer's Disease Gene Susceptibility Assessment
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Structural basis for activation of the complement system by component C4 cleavage.

Rune T Kidmose1, Nick S Laursen, József Dobó

  • 1Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.

Proceedings of the National Academy of Sciences of the United States of America
|September 6, 2012
PubMed
Summary
This summary is machine-generated.

Structural insights reveal how complement system proteins C4 and MASP-2 interact to initiate pathogen defense. This clarifies crucial steps in innate immunity for eliminating threats.

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Area of Science:

  • Immunology
  • Structural Biology
  • Biochemistry

Background:

  • The complement system is vital for innate immunity, with lectin and classical pathways recognizing pathogens.
  • Activation involves MASP-2 or C1s proteases cleaving the C4 protein, a key step in complement cascade initiation.

Purpose of the Study:

  • To elucidate the structural basis of C4 cleavage by MASP-2, a crucial step in complement activation.
  • To understand the interaction between C4 and MASP-2 at a molecular level.

Main Methods:

  • X-ray crystallography was used to determine the structures of human C4 and the C4·MASP-2 complex.
  • Site-directed mutagenesis was employed to investigate the functional significance of key interaction interfaces.

Main Results:

  • The crystal structures reveal substantial conformational changes in C4 upon binding MASP-2, ordering the scissile bond region for protease insertion.
  • MASP-2 utilizes an exosite within its CCP domains to recognize the C4 C345C domain, facilitating cleavage.
  • Mutations at the C345C-CCP interface disrupt C4-MASP-2 interaction and inhibit C4 cleavage.

Conclusions:

  • The findings provide a unified structural framework for C4 cleavage by both MASP-2 (lectin pathway) and C1s (classical pathway).
  • This understanding is essential for comprehending pathogen elimination and defense against altered self via complement activation.