Experimental Data Snapshot

  • Resolution: 2.50 Å
  • R-Value Free: 0.253 
  • R-Value Work: 0.205 
  • R-Value Observed: 0.205 

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The crystal structure of bikunin from the inter-alpha-inhibitor complex: a serine protease inhibitor with two Kunitz domains.

Xu, Y.Carr, P.D.Guss, J.M.Ollis, D.L.

(1998) J Mol Biol 276: 955-966

  • DOI: https://doi.org/10.1006/jmbi.1997.1582
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    Bikunin is a serine protease inhibitor found in the blood serum and urine of humans and other animals. Its sequence shows internal repetition, suggesting that it contains two domains that resemble bovine pancreatic trypsin inhibitor (BPTI). A fragment of bikunin has been crystallised, its structure solved and subsequently refined against 2.5 A data. The two BPTI-like domains pack closely together and are related by an approximate 60 degrees rotation combined with a translation. These domains are very similar to each other and other proteins with this fold. The largest variations occur in the loops responsible for protease recognition. The loops of the first domain are unobstructed by the remaining protein. However, the loops of the second domain are close to the first domain and it is possible that protease binding may be affected or, in some cases, abolished by the presence of the first domain. Thus, cleavage of the two domains could alter the substrate specificity of domain II. Bikunin has a hydrophobic patch close to the N terminus of domain I, which is the most likely site for cell-surface receptor binding. In addition, there is a basic patch at one end of domain II that may be responsible for the inhibition of calcium oxalate crystallization in urine.

  • Organizational Affiliation

    Research School of Chemistry, Australian National University, Canberra, Australia.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
BIKUNIN147Homo sapiensMutation(s): 0 
UniProt & NIH Common Fund Data Resources
Find proteins for P02760 (Homo sapiens)
Explore P02760 
Go to UniProtKB:  P02760
PHAROS:  P02760
GTEx:  ENSG00000106927 
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP02760
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 2.50 Å
  • R-Value Free: 0.253 
  • R-Value Work: 0.205 
  • R-Value Observed: 0.205 
  • Space Group: P 41 21 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 55.3α = 90
b = 55.3β = 90
c = 146.9γ = 90
Software Package:
Software NamePurpose
DENZOdata reduction
SCALEPACKdata scaling
X-PLORmodel building

Structure Validation

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Ligand Structure Quality Assessment 

Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 1999-03-16
    Type: Initial release
  • Version 1.1: 2008-03-24
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Non-polymer description, Version format compliance
  • Version 1.3: 2020-07-29
    Type: Remediation
    Reason: Carbohydrate remediation
    Changes: Data collection, Derived calculations, Structure summary
  • Version 1.4: 2023-08-02
    Changes: Database references, Refinement description, Structure summary