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Going full circle: Determining the structures of complement component 9.

Bradley A Spicer¹, Michelle A Dunstone¹

¹Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, VIC, Australia.

Methods in Enzymology

|March 13, 2021

Summary

This summary is machine-generated.

Pore forming proteins like complement component 9 (C9) can form soluble oligomers (polyC9) without membranes. This research details C9 protein chemistry, expression, and purification for structural studies.

Keywords:

Complement Crystallization Membrane attack complex PolyC9 Pore forming proteins Protein purification Transmission electron microscopy

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Area of Science:

Biochemistry
Structural Biology
Immunology

Background:

Pore forming proteins (PFPs) undergo conformational changes to create membrane pores.
PFPs are metastable, transitioning from soluble to membrane-bound states, but prone to aggregation.
Complement component 9 (C9) is part of the membrane attack complex (MAC), known for bacterial pore formation.

Purpose of the Study:

To discuss the protein chemistry of human C9, focusing on its unusual ability to form soluble oligomers (polyC9).
To detail the expression, purification, and structural characterization of C9 and its oligomeric form, polyC9.
To overcome challenges in studying metastable PFPs using advanced structural biology techniques.

Main Methods:

Recombinant DNA expression systems for producing C9.
Protein purification techniques for monomeric and oligomeric C9.
X-ray crystallography and single particle cryo-electron microscopy (cryo-EM) for structural analysis.

Main Results:

Successful expression and purification of recombinant C9.
Crystallization of the soluble monomeric form of C9.
Preparation and characterization of the soluble oligomeric polyC9 state.

Conclusions:

Human C9 can form soluble oligomers (polyC9) independently of membranes or other complement factors.
Advances in expression systems and high-resolution techniques enable structural studies of MAC components.
The study provides insights into the structural biology of C9 and the formation of the membrane attack complex.