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| Title | Structure and activation of C1, the complex initiating the classical pathway of the complement cascade. |
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| Journal, issue, pages | Proc Natl Acad Sci U S A, Vol. 114, Issue 5, Page 986-991, Year 2017 |
| Publish date | Jan 31, 2017 |
 Authors | Simon A Mortensen / Bjoern Sander / Rasmus K Jensen / Jan Skov Pedersen / Monika M Golas / Jens C Jensenius / Annette G Hansen / Steffen Thiel / Gregers R Andersen /  |
| PubMed Abstract | The complement system is an important antimicrobial and inflammation-generating component of the innate immune system. The classical pathway of complement is activated upon binding of the 774-kDa C1 ...The complement system is an important antimicrobial and inflammation-generating component of the innate immune system. The classical pathway of complement is activated upon binding of the 774-kDa C1 complex, consisting of the recognition molecule C1q and the tetrameric protease complex C1rs, to a variety of activators presenting specific molecular patterns such as IgG- and IgM-containing immune complexes. A canonical model entails a C1rs with its serine protease domains tightly packed together in the center of C1 and an intricate intramolecular reaction mechanism for activation of C1r and C1s, induced upon C1 binding to the activator. Here, we show that the serine protease domains of C1r and C1s are located at the periphery of the C1rs tetramer both when alone or within the nonactivated C1 complex. Our structural studies indicate that the C1 complex adopts a conformation incompatible with intramolecular activation of C1, suggesting instead that intermolecular proteolytic activation between neighboring C1 complexes bound to a complement activating surface occurs. Our results rationalize how a multitude of structurally unrelated molecular patterns can activate C1 and suggests a conserved mechanism for complement activation through the classical and the related lectin pathway. |
 External links | Proc Natl Acad Sci U S A / PubMed:28104818 / PubMed Central |
| Methods | SAS (X-ray synchrotron) |
| Structure data |  SASDB38: |
| Source |
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Homo sapiens (human)