Experimental Data Snapshot

  • Resolution: 2.92 Å
  • R-Value Free: 0.252 
  • R-Value Work: 0.208 
  • R-Value Observed: 0.211 

wwPDB Validation   3D Report Full Report

This is version 1.4 of the entry. See complete history


Structural basis of the C1q/C1s interaction and its central role in assembly of the C1 complex of complement activation.

Venkatraman Girija, U.Gingras, A.R.Marshall, J.E.Panchal, R.Sheikh, M.A.Gal, P.Schwaeble, W.J.Mitchell, D.A.Moody, P.C.Wallis, R.

(2013) Proc Natl Acad Sci U S A 110: 13916-13920

  • DOI: https://doi.org/10.1073/pnas.1311113110
  • Primary Citation of Related Structures:  
    4LMF, 4LOR, 4LOS, 4LOT

  • PubMed Abstract: 

    Complement component C1, the complex that initiates the classical pathway of complement activation, is a 790-kDa assembly formed from the target-recognition subcomponent C1q and the modular proteases C1r and C1s. The proteases are elongated tetramers that become more compact when they bind to the collagen-like domains of C1q. Here, we describe a series of structures that reveal how the subcomponents associate to form C1. A complex between C1s and a collagen-like peptide containing the C1r/C1s-binding motif of C1q shows that the collagen binds to a shallow groove via a critical lysine side chain that contacts Ca(2+)-coordinating residues. The data explain the Ca(2+)-dependent binding mechanism, which is conserved in C1r and also in mannan-binding lectin-associated serine proteases, the serine proteases of the lectin pathway activation complexes. In an accompanying structure, C1s forms a compact ring-shaped tetramer featuring a unique head-to-tail interaction at its center that replicates the likely arrangement of C1r/C1s polypeptides in the C1 complex. Additional structures reveal how C1s polypeptides are positioned to enable activation by C1r and interaction with the substrate C4 inside the cage-like assembly formed by the collagenous stems of C1q. Together with previously determined structures of C1r fragments, the results reported here provide a structural basis for understanding the early steps of complement activation via the classical pathway.

  • Organizational Affiliation

    Department of Infection, University of Leicester, Leicester LE1 9HN, United Kingdom.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Complement C1s subcomponent heavy chain
A, B, C, D
276Homo sapiensMutation(s): 0 
Gene Names: C1S
UniProt & NIH Common Fund Data Resources
Find proteins for P09871 (Homo sapiens)
Explore P09871 
Go to UniProtKB:  P09871
PHAROS:  P09871
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP09871
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 2 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
Query on CA

Download Ideal Coordinates CCD File 
F [auth A]
G [auth A]
H [auth A]
J [auth B]
K [auth B]
F [auth A],
G [auth A],
H [auth A],
J [auth B],
K [auth B],
L [auth B],
N [auth C],
O [auth C],
P [auth C],
R [auth D],
S [auth D],
T [auth D]
Query on NA

Download Ideal Coordinates CCD File 
E [auth A],
I [auth B],
M [auth C],
Q [auth D]
Experimental Data & Validation

Experimental Data

  • Resolution: 2.92 Å
  • R-Value Free: 0.252 
  • R-Value Work: 0.208 
  • R-Value Observed: 0.211 
  • Space Group: P 1 21 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 67.876α = 90
b = 71.668β = 95.93
c = 157.723γ = 90
Software Package:
Software NamePurpose
PDB_EXTRACTdata extraction
StructureStudiodata collection
MOSFLMdata reduction
SCALAdata scaling

Structure Validation

View Full Validation Report

Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2013-08-07
    Type: Initial release
  • Version 1.1: 2013-08-28
    Changes: Database references
  • Version 1.2: 2013-09-04
    Changes: Database references
  • Version 1.3: 2013-10-23
    Changes: Database references
  • Version 1.4: 2018-01-24
    Changes: Structure summary