Structure of complement C3(H₂O) revealed by quantitative cross-linking/mass spectrometry and modeling

Abstract

The slow but spontaneous and ubiquitous formation of C3(H 2 O), the hydrolytic and conformationally rearranged product of C3, initiates antibody-independent activation of the complement system that is a key first line of antimicrobial defense. The structure of C3(H 2 O) has not been determined. Here we subjected C3(H 2 O) to quantitative cross-linking/mass spectrometry (QCLMS). This revealed details of the structural differences and similarities between C3(H 2 O) and C3, as well as between C3(H 2 O) and its pivotal proteolytic cleavage product, C3b, which shares functionally similarity with C3(H 2 O). Considered in combination with the crystal structures of C3 and C3b, the QCMLS data suggest that C3(H 2 O) generation is accompanied by the migration of the thioester-containing domain of C3 from one end of the molecule to the other. This creates a stable C3b-like platform able to bind the zymogen, factor B, or the regulator, factor H. Integration of available crystallographic and QCLMS data allowed the determination of a 3D model of the C3(H 2 O) domain architecture. The unique arrangement of domains thus observed in C3(H 2 O), which retains the anaphylatoxin domain (that is excised when C3 is enzymatically activated to C3b), can be used to rationalize observed differences between C3(H 2 O) and C3b in terms of complement activation and regulation. Molecular & Cellular Proteomics

Cross-linking mass spectrometry: methods and applications in structural, molecular and systems biology

“…2c). Early applications of this method were to investigate the conformational changes that take place after spontaneous hydrolysis of a thioester bond in the complement protein C3 46 and the impact of phosphorylation on the conformation of an F-type ATPase, by comparing crosslinks derived from complexes treated with either BS3-d0 or BS3-d4 47 . The relative abundances of the cross-links were compared manually.…”

Integrative structure modeling with the Integrative Modeling Platform

“…We will utilize chemical cross‐linking coupled with mass spectrometry, negative‐stain EM, and X‐ray crystallography data to reconstruct this stalk, hypothesizing that we know already the structure of the core. The example can be easily generalized to any other set of subunits …”

“…Using PMI, the entire modeling protocol can be described with a set of Python scripts, which are typically deposited, together with the input data and output models, in a publicly available repository, such as GitHub and the nascent Protein Data Bank (PDB) archive of integrative structures (https://pdb-dev.wwpdb.org/); for examples, see Refs. , and .…”

Profile of the Hydrolysis of the C3 Component of Complement Is a Biochemical Marker of Cancer?

“…Одной из значимых его особенностей является способность ковалентно присоединяться к акцепторным молекулам на поверхности клетки через эфирную или амидную свя-зи [3,4]. Это свойство C3 проявляет благо-даря наличию внутримолекулярной тиоэ-фирной связи в α-цепи.…”