Periodic Reporting for period 4 - Controlling MAC (Structural basis of controlling the membrane attack complex)
Période du rapport: 2025-01-01 au 2025-06-30
Complement is a blood based immune network that plays an important role in innate and adaptive immune responses. Activation of complement culminates in the formation of a large lytic pore called the Membrane Attack Complex (MAC), which assembles on lipid bilayers and punches holes in target cells. MAC is a versatile and highly effective immune effector as there is no specific receptor directing MAC to pathogens. However, human cells are susceptible to damage by MAC if not properly controlled. Dysregulation of MAC on human cells can have devastating impact for disease pathologies including haemolytic anaemia and immune evasion strategies by cancer cells. Understanding how MAC is controlled during an immune response will enable the design of therapeutics that have the potential to precisely regulate complement activity and improve human health.
The objective of CONTROLLING MAC is to uncover the fundamental molecular principles underpinning MAC regulation on human cells. To achieve this ambitious goal, Controlling MAC uses a range of structural biology and biophysical tools to understand how complement activation impacts cellular pathways that modulate inflammation. The project develops an innovative approach to exploring the interactions between complement proteins and their local lipid environment. The novel insights from these experiments will explain how conformational changes in protein structure are linked with changes in physical properties of cellular membranes. Together, these data will explain how MAC is regulated and define a new role for lipids in immune homeostasis.
The conclusions of the project provide a structural basis for how MAC is regulated on human cells when the immune system switches on. Our cryo electron microscopy (cryoEM) structure of a soluble regulated form of MAC shows how the blood-based chaperone, clusterin, wraps across the polymerizing face of MAC and defines a new conformation of C9. Additionally, our structural work defines a key mechanism of action for CD59, the only membrane-bound regulator of MAC-mediated cell death. By developing a model lipid-based system and using it for structural studies, we explain how CD59 catches and deflects the transmembrane beta-hairpins of MAC proteins to prevent membrane damage. Finally, by developing novel macrocyclic peptides that target CD59 we provide a blueprint for the design of future therapeutics that have the potential to regulate complement activity and improve human health.
The objective of CONTROLLING MAC is to uncover the fundamental molecular principles underpinning MAC regulation on human cells. To achieve this ambitious goal, Controlling MAC uses a range of structural biology and biophysical tools to understand how complement activation impacts cellular pathways that modulate inflammation. The project develops an innovative approach to exploring the interactions between complement proteins and their local lipid environment. The novel insights from these experiments will explain how conformational changes in protein structure are linked with changes in physical properties of cellular membranes. Together, these data will explain how MAC is regulated and define a new role for lipids in immune homeostasis.
The conclusions of the project provide a structural basis for how MAC is regulated on human cells when the immune system switches on. Our cryo electron microscopy (cryoEM) structure of a soluble regulated form of MAC shows how the blood-based chaperone, clusterin, wraps across the polymerizing face of MAC and defines a new conformation of C9. Additionally, our structural work defines a key mechanism of action for CD59, the only membrane-bound regulator of MAC-mediated cell death. By developing a model lipid-based system and using it for structural studies, we explain how CD59 catches and deflects the transmembrane beta-hairpins of MAC proteins to prevent membrane damage. Finally, by developing novel macrocyclic peptides that target CD59 we provide a blueprint for the design of future therapeutics that have the potential to regulate complement activity and improve human health.
CONTROLLING MAC has delivered on all three of its main major research initiatives. The first focuses on the role of a cell surface receptor, CD59, in preventing MAC assembly on human cells. Using cryo electron microscopy to visualize CD59-inhibited MAC assembly precursors, we discover that CD59 blocks cell damage by redirecting the trajectory of transmembrane residues of MAC. In addition, we created novel macrocyclic peptides that mimic this interaction and regulate complement activity in diverse cellular contexts. Finally, the third research stream uncovers the role of blood-based chaperones in capturing and clearing potentially harmful MAC activation by-products. Our structural data explain how clusterin blocks polymerizing cargo through electrostatic interactions and provide evidence into how cell clearance pathways mediate immune homeostasis. These results have been disseminated through pre-prints, publication in open access peer reviewed journals, and presented at international conferences. Structural biology and mass spectrometry data supporting these publications have been deposited in publicly available repositories.
CONTROLLING MAC pushes the state of the art in structural immunology. The project developed a novel model membrane system and new macrocyclic peptide tools to probe the molecular basis for MAC regulation. By applying innovative computational strategies in we solved multiple structures of what was previously thought to be a single immune complex. The results achieved for all the three work packages have advanced our understanding of MAC inhibition on human cells and the role of blood-based chaperones in modulating inflammation during an immune response.