title: The complement components of the major histocompatibility locus.
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.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001327:Autoimmune Diseases / Q000235:genetics; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics; D055598:Chemical Phenomena; D002621:Chemistry; D003167:Complement Activation; D003175:Complement C2 / Q000235:genetics; D003176:Complement C3 / Q000235:genetics; D050577:Complement C3-C5 Convertases; D003179:Complement C3b / Q000235:genetics; D003181:Complement C4 / Q000235:genetics; D003165:Complement System Proteins / Q000235:genetics* / Q000502:physiology; D004247:DNA; D004274:DNA, Recombinant; D004952:Esters; D005796:Genes; D006801:Humans; D016167:Integrin alphaXbeta2; D008285:Major Histocompatibility Complex; D051379:Mice; D008970:Molecular Weight; D011110:Polymorphism, Genetic; D011951:Receptors, Complement / Q000235:genetics; D017463:Receptors, Complement 3b; D013438:Sulfhydryl Compounds
chemical_list: D002352:Carrier Proteins; D003175:Complement C2; D003176:Complement C3; D003181:Complement C4; D004274:DNA, Recombinant; D004952:Esters; D016167:Integrin alphaXbeta2; D011951:Receptors, Complement; D017463:Receptors, Complement 3b; D013438:Sulfhydryl Compounds; D003179:Complement C3b; D003165:Complement System Proteins; D004247:DNA; D050577:Complement C3-C5 Convertases