Biological Assembly 1  

 3D View: Structure | Electron Density | Ligand Interaction

Global Symmetry: Asymmetric - C1 
Global Stoichiometry: Hetero 3-mer - A1BC Pseudo Symmetry: Cyclic - C3  (3D View)
Pseudo Stoichiometry: Homo 3-mer - A3 

Biological assembly 1 assigned by authors and generated by PISA (software)

Macromolecule Content

• Total Structure Weight: 44.25 kDa 
• Atom Count: 3314 
• Residue Count: 394 
• Unique protein chains: 3

1PK6

Globular Head of the Complement System Protein C1q

• DOI: 10.2210/pdb1PK6/pdb

• Classification: IMMUNE SYSTEM
• Organism(s): Homo sapiens
• Mutation(s): No 


• Deposited: 2003-06-05 Released: 2003-10-21 
• Deposition Author(s): Gaboriaud, C., Juanhuix, J., Gruez, A., Lacroix, M., Darnault, C., Pignol, D., Verger, D., Fontecilla-Camps, J.C., Arlaud, G.J.

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Experimental Data Snapshot

• Method: X-RAY DIFFRACTION
• Resolution: 1.85 Å
• R-Value Free: 0.239 
• R-Value Work: 0.199 
• R-Value Observed: 0.201 

Literature

The crystal structure of the globular head of complement protein C1q provides a basis for its versatile recognition properties.

Gaboriaud, C., Juanhuix, J., Gruez, A., Lacroix, M., Darnault, C., Pignol, D., Verger, D., Fontecilla-Camps, J.C., Arlaud, G.J.

(2003) J Biol Chem 278: 46974-46982

• PubMed: 12960167 
• DOI: 10.1074/jbc.M307764200
• Structures With Same Primary Citation


• PubMed Abstract: 
  

C1q is a versatile recognition protein that binds to an amazing variety of immune and non-immune ligands and triggers activation of the classical pathway of complement. The crystal structure of the C1q globular domain responsible for its recognition properties has now been solved and refined to 1.9 A of resolution. The structure reveals a compact, almost spherical heterotrimeric assembly held together mainly by non-polar interactions, with a Ca2+ ion bound at the top. The heterotrimeric assembly of the C1q globular domain appears to be a key factor of the versatile recognition properties of this protein. Plausible three-dimensional models of the C1q globular domain in complex with two of its physiological ligands, C-reactive protein and IgG, are proposed, highlighting two of the possible recognition modes of C1q. The C1q/human IgG1 model suggests a critical role for the hinge region of IgG and for the relative orientation of its Fab domain in C1q binding.

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Organizational Affiliation: 

Laboratoire de Cristallographie et Cristallogéncse des Protéines, Institut de Biologie Structurale Jean-Pierre Ebel, Commissariat à l'Energie Atomique (CEA)-CNRS-Université Joseph Fourier, 41 rue Jules Horowitz, 38027 Grenoble Cedex 1, France.

Macromolecules

Entity ID: 1
Molecule	Chains	Sequence Length	Organism	Details
Complement C1q subcomponent, A chain precursor	A	133	Homo sapiens	Mutation(s): 0  Gene Names: C1QA
Find proteins for P02745 (Homo sapiens) Explore P02745  Go to UniProtKB:  P02745
NIH Common Fund Data Resources
PHAROS  P02745 GTEx  ENSG00000173372

Entity ID: 2
Molecule	Chains	Sequence Length	Organism	Details
Complement C1q subcomponent, B chain precursor	B	132	Homo sapiens	Mutation(s): 0  Gene Names: C1QB
Find proteins for P02746 (Homo sapiens) Explore P02746  Go to UniProtKB:  P02746
NIH Common Fund Data Resources
PHAROS  P02746 GTEx  ENSG00000173369

Entity ID: 3
Molecule	Chains	Sequence Length	Organism	Details
Complement C1q subcomponent, C chain precursor	C	129	Homo sapiens	Mutation(s): 0  Gene Names: C1QC, C1QG
Find proteins for P02747 (Homo sapiens) Explore P02747  Go to UniProtKB:  P02747
NIH Common Fund Data Resources
PHAROS  P02747 GTEx  ENSG00000159189

Small Molecules

Ligands 1 Unique
ID	Chains	Name / Formula / InChI Key	2D Diagram
CA	B	CALCIUM ION Ca BHPQYMZQTOCNFJ-UHFFFAOYSA-N

Experimental Data & Validation

Experimental Data

• Method: X-RAY DIFFRACTION
• Resolution: 1.85 Å
• R-Value Free: 0.239 
• R-Value Work: 0.199 
• R-Value Observed: 0.201 
• Space Group: C 1 2 1

Unit Cell:

Length ( Å )	Angle ( ˚ )
a = 80.182	α = 90
b = 53.222	β = 112.32
c = 90.88	γ = 90

Software Package:

Software Name	Purpose
REFMAC	refinement
XDS	data reduction
CCP4	data scaling
AMoRE	phasing

Structure Validation

Entry History 

Deposition Data

• Deposited Date: 2003-06-05 
• Released Date: 2003-10-21 
Deposition Author(s): Gaboriaud, C., Juanhuix, J., Gruez, A., Lacroix, M., Darnault, C., Pignol, D., Verger, D., Fontecilla-Camps, J.C., Arlaud, G.J.

Revision History 

• Version 1.0: 2003-10-21
  Type: Initial release
  
• Version 1.1: 2008-04-29
  Changes: Version format compliance
• Version 1.2: 2011-07-13
  Changes: Version format compliance
• Version 1.3: 2018-01-31
  Changes: Advisory, Experimental preparation