The X-ray crystal structure of human complement protease C1s zymogen

Experimental Data Snapshot

  • Resolution: 2.66 Å
  • R-Value Free: 0.259 
  • R-Value Work: 0.201 
  • R-Value Observed: 0.203 

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A Molecular Switch Governs the Interaction between the Human Complement Protease C1s and Its Substrate, Complement C4.

Perry, A.J.Wijeyewickrema, L.C.Wilmann, P.G.Gunzburg, M.J.D'Andrea, L.Irving, J.A.Pang, S.S.Duncan, R.C.Wilce, J.A.Whisstock, J.C.Pike, R.N.

(2013) J Biol Chem 288: 15821-15829

  • DOI: https://doi.org/10.1074/jbc.M113.464545
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    The complement system is an ancient innate immune defense pathway that plays a front line role in eliminating microbial pathogens. Recognition of foreign targets by antibodies drives sequential activation of two serine proteases, C1r and C1s, which reside within the complement Component 1 (C1) complex. Active C1s propagates the immune response through its ability to bind and cleave the effector molecule complement Component 4 (C4). Currently, the precise structural and biochemical basis for the control of the interaction between C1s and C4 is unclear. Here, using surface plasmon resonance, we show that the transition of the C1s zymogen to the active form is essential for C1s binding to C4. To understand this, we determined the crystal structure of a zymogen C1s construct (comprising two complement control protein (CCP) domains and the serine protease (SP) domain). These data reveal that two loops (492-499 and 573-580) in the zymogen serine protease domain adopt a conformation that would be predicted to sterically abrogate C4 binding. The transition from zymogen to active C1s repositions both loops such that they would be able to interact with sulfotyrosine residues on C4. The structure also shows the junction of the CCP1 and CCP2 domains of C1s for the first time, yielding valuable information about the exosite for C4 binding located at this position. Together, these data provide a structural explanation for the control of the interaction with C1s and C4 and, furthermore, point to alternative strategies for developing therapeutic approaches for controlling activation of the complement cascade.

  • Organizational Affiliation

    Department of Biochemistry and Molecular Biology, Monash University, Clayton, Melbourne, Victoria 3800, Australia.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Complement C1s subcomponent
A, B
397Homo sapiensMutation(s): 2 
Gene Names: C1S
UniProt & NIH Common Fund Data Resources
Find proteins for P09871 (Homo sapiens)
Explore P09871 
Go to UniProtKB:  P09871
PHAROS:  P09871
GTEx:  ENSG00000182326 
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP09871
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 2.66 Å
  • R-Value Free: 0.259 
  • R-Value Work: 0.201 
  • R-Value Observed: 0.203 
  • Space Group: C 2 2 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 149.89α = 90
b = 158.9β = 90
c = 78.7γ = 90
Software Package:
Software NamePurpose
ADSCdata collection
XDSdata reduction
Aimlessdata scaling

Structure Validation

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Entry History 

Revision History  (Full details and data files)

  • Version 1.0: 2013-04-24
    Type: Initial release
  • Version 1.1: 2013-05-01
    Changes: Database references
  • Version 1.2: 2013-06-19
    Changes: Database references
  • Version 1.3: 2013-07-03
    Changes: Structure summary
  • Version 1.4: 2023-09-20
    Changes: Data collection, Database references, Refinement description