Crystal Structure of Human Complement Protein C8gamma at 1.2 A Resolution

Experimental Data Snapshot

  • Resolution: 1.20 Å
  • R-Value Free: 0.229 
  • R-Value Work: 0.223 
  • R-Value Observed: 0.223 

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Crystal structure of human complement protein C8gamma at 1.2 A resolution reveals a lipocalin fold and a distinct ligand binding site.

Ortlund, E.Parker, C.L.Schreck, S.F.Ginell, S.Minor, W.Sodetz, J.M.Lebioda, L.

(2002) Biochemistry 41: 7030-7037

  • DOI: https://doi.org/10.1021/bi025696i
  • Primary Citation of Related Structures:  
    1IW2, 1LF7

  • PubMed Abstract: 

    C8gamma is a 22-kDa subunit of human C8, which is one of five components of the cytolytic membrane attack complex of complement (MAC). C8gamma is disulfide-linked to a C8alpha subunit that is noncovalently associated with a C8beta chain. In the present study, the three-dimensional structure of recombinant C8gamma was determined by X-ray diffraction to 1.2 A resolution. The structure displays a typical lipocalin fold forming a calyx with a distinct binding pocket that is indicative of a ligand-binding function for C8gamma. When compared to other lipocalins, the overall structure is most similar to neutrophil gelatinase associated lipocalin (NGAL), a protein released from granules of activated neutrophils. Notable differences include a much deeper binding pocket in C8gamma as well as variation in the identity and position of residues lining the pocket. In C8gamma, these residues allow ligand access to a large hydrophobic cavity at the base of the calyx, whereas corresponding residues in NGAL restrict access. This suggests the natural ligands for C8gamma and NGAL are significantly different in size. Cys40 in C8gamma, which forms the disulfide bond to C8alpha, is located in a partially disordered loop (loop 1, residues 38-52) near the opening of the calyx. Access to the calyx may be regulated by movement of this loop in response to conformational changes in C8alpha during MAC formation.

  • Organizational Affiliation

    Department of Chemistry and Biochemistry and the School of Medicine, University of South Carolina, Columbia, South Carolina 29208, USA.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Complement Protein C8gamma182Homo sapiensMutation(s): 1 
Gene Names: 9q34.3
Membrane Entity: Yes 
UniProt & NIH Common Fund Data Resources
Find proteins for P07360 (Homo sapiens)
Explore P07360 
Go to UniProtKB:  P07360
PHAROS:  P07360
GTEx:  ENSG00000176919 
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP07360
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 1 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
Query on CIT

Download Ideal Coordinates CCD File 
C6 H8 O7
Experimental Data & Validation

Experimental Data

  • Resolution: 1.20 Å
  • R-Value Free: 0.229 
  • R-Value Work: 0.223 
  • R-Value Observed: 0.223 
  • Space Group: P 21 21 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 42.448α = 90
b = 58.993β = 90
c = 72.053γ = 90
Software Package:
Software NamePurpose
HKL-2000data collection
HKL-2000data reduction
RESOLVEmodel building
HKL-2000data scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2002-06-12
    Type: Initial release
  • Version 1.1: 2008-04-28
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Version format compliance
  • Version 1.3: 2018-02-14
    Changes: Data collection, Experimental preparation
  • Version 1.4: 2021-11-10
    Changes: Database references, Derived calculations
  • Version 1.5: 2022-04-13
    Changes: Database references, Structure summary