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The complement components of the major histocompatibility locus
Insights
Genetic mapping of complement component genes reveals their unique structures and functions. These studies link gene locations to inherited diseases, advancing our understanding of the human genome.
Area of Science:
- Immunogenetics
- Molecular Genetics
- Biochemistry
Background:
- Polymorphism and inherited deficiencies of complement components aid in mapping their structural genes.
- Human complement genes C2, C4, and factor B are located on chromosome 6, linked to HLA loci.
- Murine C4 gene is mapped to chromosome 17, between H2-I and H2-D.
Purpose of the Study:
- To map the structural genes of complement components.
- To elucidate the unique structural and functional characteristics of complement proteins.
- To investigate the relationship between complement gene defects and inherited diseases.
Main Methods:
- Analysis of complement component polymorphism (antigenic specificity, electrophoretic mobility).
- Gene mapping studies utilizing human and murine genetic markers.
- Structural and molecular genetic investigations of complement proteins.
Main Results:
- Established gene locations for C2, C4, and factor B in humans and C4 in mice.
- Identified C2 and factor B as novel serine proteases crucial for complement pathways.
- Revealed an intrachain thioester bond in C4 essential for hemolytic activity.
Conclusions:
- Complement gene mapping provides insights into their structural organization and evolutionary relationships.
- Understanding complement gene structure and function is vital for clarifying associations with inherited human diseases.
- Molecular genetic studies are key to deciphering the role of complement system defects in disease pathogenesis.
Abstract:
Polymorphism of complement components, recognized by differences in either their antigenic specificity or their electrophoretic mobility, together with studies of inherited deficiencies, has enabled many of their structural genes to be mapped. In humans, three genes (for C2, C4, and factor B) have been placed between HLA-D and HLA-B on chromosome 6 and in mice, C4 between H2-I and H2-D, chromosome 17. Structural studies show that these components have exceptional features. C2 and factor B which contain the proteolytic active site of the C3 and C5 convertases are of the classical and alternative pathway respectively and are similar in structure and function. Both are novel types of serine proteases. C4 (as C3) contains an intrachain thioester bond essential for hemolytic activity. Molecular genetic investigations are determining the relative positions of these genes, and their precise structure, and should clarify their relation to the inherited diseases which are associated with defects in this section of the human genome.