Related Experiment Videos
Conformational changes of the subunits C1q, C1r and C1s of human complement component C1 demonstrated by 125I
Insights
Radioiodination revealed distinct labeling patterns for complement C1r and C1s enzymes. Complement C1r undergoes significant conformational changes upon activation, impacting its labeling distribution.
Area of Science:
- Biochemistry
- Immunology
- Complement System
Background:
- The complement system is crucial for innate and adaptive immunity.
- Understanding the activation and structure of complement component C1 is vital for immune response.
- C1 is a complex composed of C1q, C1r, and C1s, initiating the classical complement pathway.
Purpose of the Study:
- To investigate the distribution of radioiodine labeling in the heavy (H) and light (L) chains of complement C1r and C1s enzymes.
- To examine how activation and complex formation with other C1 components affect the labeling patterns of C1r and C1q.
Main Methods:
- Proteins C1s, C1r (proenzyme and enzyme forms), and C1q were labeled with radioiodine (125I).
- The distribution of the 125I label was analyzed between the H- and L-chains of C1s and C1r under various conditions (activation, presence of other C1 components).
Main Results:
- Approximately 90% of the 125I label in C1s was found in the H-chain, with minimal dependence on activation state.
- In C1r proenzyme, 50% of the label was in the H-chain, but this shifted to 10% in activated C1r, with 90% in the L-chain.
- The presence of C1s, C1q, or C1qs reduced C1r H-chain labeling, while C1s or C1rs enhanced C1q 125I uptake, contrary to expectations.
Conclusions:
- Complement C1r and C1q proteins undergo conformational alterations during activation and C1 complex formation.
- Labeling patterns provide insights into the structural dynamics of C1r and C1q during complement activation.
- The unexpected enhancement of C1q labeling suggests complex structural rearrangements within the C1 complex.
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.