Gadeberg Trine Amalie Fogh, Jørgensen Martin Høgholm, Olesen Heidi Gytz, Lorentzen Josefine, Harwood Seandean Lykke, Almeida Ana Viana, Fruergaard Marlene Uglebjerg, Jensen Rasmus Kjeldsen, Kanis Philipp, Pedersen Henrik, Tranchant Emil, Petersen Steen Vang, Thøgersen Ida Buch, Kragelund Birthe Brandt, Lyons Joseph Anthony, Enghild Jan Johannes, Andersen Gregers Rom
Department of Molecular Biology and Genetics, Aarhus, Denmark.
Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
Nat Struct Mol Biol. 2025 May;32(5):884-895. doi: 10.1038/s41594-024-01467-4. Epub 2025 Jan 23.
The C3 protein is the central molecule within the complement system and undergoes proteolytic activation to C3b in the presence of pathogens. Pattern-independent activation of C3 also occurs via hydrolysis, resulting in C3(HO), but the structural details of C3 hydrolysis remain elusive. Here we show that the conformation of the C3(HO) analog, C3MA, is indistinguishable from C3b. In contrast, the reaction intermediate C3* adopts a conformation dramatically different from both C3 and C3MA. In C3*, unlocking of the macroglobulin (MG) 3 domain creates a large opening in the MG ring through which the anaphylatoxin (ANA) domain translocates through a transient opening. C3MA formation is inhibited by an MG3-specific nanobody and prevented by linking the ANA domain to the C3 β-chain. Our study reveals an unexpected dynamic behavior of C3 and forms the basis for elucidation of the in vivo contribution of C3 hydrolysis and for controlling complement upon intravascular hemolysis and surface-contact-induced activation.
C3蛋白是补体系统的核心分子，在病原体存在的情况下会发生蛋白水解激活成为C3b。C3也会通过水解进行不依赖模式的激活，生成C3(HO)，但C3水解的结构细节仍不清楚。在此我们表明，C3(HO)类似物C3MA的构象与C3b无法区分。相比之下，反应中间体C3采用的构象与C3和C3MA都有显著不同。在C3中，巨球蛋白（MG）3结构域的解锁在MG环中形成了一个大开口，过敏毒素（ANA）结构域通过这个瞬时开口发生易位。C3MA的形成受到一种MG3特异性纳米抗体的抑制，并且通过将ANA结构域与C3β链连接而被阻止。我们的研究揭示了C3意想不到的动态行为，并为阐明C3水解在体内的作用以及在血管内溶血和表面接触诱导激活时控制补体奠定了基础。
