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Updated: Apr 27, 2026
From Constructs to Crystals – Towards Structure Determination of β-barrel Outer Membrane Proteins
Published on: July 4, 2016
Crystallization and preliminary crystallographic studies of the complement 1qA globular domain from zebrafish,
Hongyu Yuan1, Rong Chen1, Yanjie Liu1
1Department of Microbiology and Immunology, College of Veterinary Medicine, China Agricultural University, Beijing 100193, People's Republic of China.
Insights
Researchers determined the structure of zebrafish C1qA globular domain, offering insights into fish immune system components. This structural data aids understanding of C1qA in diverse fish species.
Area of Science:
- Structural biology
- Immunology
- Biochemistry
Background:
- Complement 1q (C1q) initiates the classical complement pathway in vertebrates.
- Human C1q globular domain (C1qgD) structure is known, but fish C1qgD structure remains uncharacterized.
- Fish C1q shares functional and genomic similarities with mammalian C1q.
Purpose of the Study:
- To elucidate the three-dimensional structure of the zebrafish C1qA globular domain (Dare-C1qAgD).
- To provide structural insights into C1qA function in fish species.
Main Methods:
- Expression and purification of recombinant Dare-C1qAgD.
- Crystallization of Dare-C1qAgD.
- X-ray diffraction data collection and analysis to determine crystal structure.
Main Results:
- Dare-C1qAgD was successfully crystallized.
- X-ray diffraction data were collected to a resolution of 2.05 Å.
- The crystal belonged to the orthorhombic space group P2₁2₁2₁ with specific unit-cell parameters, containing three molecules in the asymmetric unit.
Conclusions:
- The determined structure provides the first atomic-level view of a fish C1qA globular domain.
- This structural information is crucial for understanding the molecular mechanisms of the complement system in fish.
- The findings contribute to comparative structural biology of the complement system across vertebrates.
Abstract:
Complement 1q (C1q) is the first component of the complement system which can initiate the classical complement pathway. In human, C1q is composed of 18 polypeptide chains: six C1qA chains, six C1qB chains and six C1qC chains. Each chain has a signal peptide and is comprised of a collagen-like region and a C-terminal C1q globular domain (C1qgD), which is organized as a heterotrimer. C1qgD can recognize antigen-antibody complexes containing IgG and IgM or can bind directly to the C-reactive protein. Although the classical complement pathway is found from fish to mammals, only the human C1qgD structure has been determined. Compared with that of mammals, fish C1q exhibits similar immune functions and genome arrangement. In order to illustrate the structure of C1qgD in fish, zebrafish (Danio rerio) C1qA globular domain (Dare-C1qAgD) was expressed, purified and crystallized. X-ray diffraction data were collected from a crystal to a resolution of 2.05 Å; the crystal belonged to the orthorhombic space group P2₁2₁2₁, with unit-cell parameters a=50.347, b=85.059, c=95.560 Å. It contained three molecules in the asymmetric unit. The Matthews coefficient value VM was 2.31 Å3 Da(-1), with a calculated solvent content of 46.7%. The data will help to give insight into the structural basis of C1qA in fish species.
