8W18

The crystal structure of the Michaelis-Menten complex of a C1s/C1-INH at 3.94 Angstroms

This is a non-PDB format compatible entry.

Summary for 8W18

• Entry DOI: 10.2210/pdb8w18/pdb
• Descriptor: Plasma protease C1 inhibitor, Complement C1s subcomponent light chain, Complement C1s subcomponent heavy chain (3 entities in total)
• Functional Keywords: complement, c1s, c1 esterase inhibitor, michaelis complex, reactive center loop, exosite, immune system
• Biological source: Homo sapiens (human); More
• Total number of polymer chains: 3
• Total formula weight: 88254.47

Authors

Garrigues, R.J.,Garcia, B.L. (deposition date: 2024-02-15, release date: 2024-06-26, Last modification date: 2024-10-30)

Primary citation

Garrigues, R.J.,Garrison, M.P.,Garcia, B.L.
The Crystal Structure of the Michaelis-Menten Complex of C1 Esterase Inhibitor and C1s Reveals Novel Insights into Complement Regulation.
J Immunol., 213:718-729, 2024

PubMed Abstract: The ancient arm of innate immunity known as the complement system is a blood proteolytic cascade involving dozens of membrane-bound and solution-phase components. Although many of these components serve as regulatory molecules to facilitate controlled activation of the cascade, C1 esterase inhibitor (C1-INH) is the sole canonical complement regulator belonging to a superfamily of covalent inhibitors known as serine protease inhibitors (SERPINs). In addition to its namesake role in complement regulation, C1-INH also regulates proteases of the coagulation, fibrinolysis, and contact pathways. Despite this, the structural basis for C1-INH recognition of its target proteases has remained elusive. In this study, we present the crystal structure of the Michaelis-Menten (M-M) complex of the catalytic domain of complement component C1s and the SERPIN domain of C1-INH at a limiting resolution of 3.94 Å. Analysis of the structure revealed that nearly half of the protein/protein interface is formed by residues outside of the C1-INH reactive center loop. The contribution of these residues to the affinity of the M-M complex was validated by site-directed mutagenesis using surface plasmon resonance. Parallel analysis confirmed that C1-INH-interfacing residues on C1s surface loops distal from the active site also drive affinity of the M-M complex. Detailed structural comparisons revealed differences in substrate recognition by C1s compared with C1-INH recognition and highlight the importance of exosite interactions across broader SERPIN/protease systems. Collectively, this study improves our understanding of how C1-INH regulates the classical pathway of complement, and it sheds new light on how SERPINs recognize their cognate protease targets.

PubMed: 38995166
DOI: 10.4049/jimmunol.2400194

Experimental method

X-RAY DIFFRACTION (3.94 Å)