title: Conformational changes of the subunits C1q, C1r and C1s of human complement component C1 demonstrated by 125I labeling.
abstract: C1s and C1r proenzymes and enzymes (C1s, C1r) and C1q were labeled with 125I. The distribution of the 125I label between H- and L-chain of C1s was only slightly dependent on the state of activation of C1s, and approx. 90% of the label was found in the H-chain. In the C1r proenzyme molecules 50% of the label was incorporated into the H-chain. The C1r H-chain label was reduced to 10% on activation of C1r to C1r, while the L-chain label increased to 90% of the total label. The presence of either C1s, C1q or C1qs during labeling reduced the C1r H-chain level, although C1r remained in the proenzyme form. The presence of C1s or C1rs enhanced the 125I uptake of C1q in Ca2+ or EDTA medium. This was unexpected because one would have anticipated a diminution of the C1q label due to the apposition of C1r and C1s, similarly as it occurs during C1rs complex and C1s dimer formation for the H-chain label of C1s. The results show that C1r and C1q alter their conformation during activation and C1 complex formation.
mesh_terms: D002118:Calcium / Q000494:pharmacology; D003166:Complement Activating Enzymes / Q000378:metabolism*; D003172:Complement C1 / Q000378:metabolism*; D015922:Complement C1q; D015923:Complement C1r; D003173:Complement C1s; D004492:Edetic Acid / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004792:Enzyme Precursors / Q000378:metabolism*; D006801:Humans; D007457:Iodine Radioisotopes; D046911:Macromolecular Substances; D011487:Protein Conformation
chemical_list: D003172:Complement C1; D004792:Enzyme Precursors; D007457:Iodine Radioisotopes; D046911:Macromolecular Substances; D015922:Complement C1q; D004492:Edetic Acid; D003166:Complement Activating Enzymes; D015923:Complement C1r; D003173:Complement C1s; D002118:Calcium