Experimental Data Snapshot

  • Resolution: 2.40 Å

Starting Model: experimental
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The molecular structure of the complex of Ascaris chymotrypsin/elastase inhibitor with porcine elastase.

Huang, K.Strynadka, N.C.Bernard, V.D.Peanasky, R.J.James, M.N.

(1994) Structure 2: 679-689

  • DOI: https://doi.org/10.1016/s0969-2126(00)00068-x
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    The intestinal parasitic worm, Ascaris suum, produces a variety of protein inhibitors that defend the organism against the host's proteinases. Eight different proteins from Ascaris suum have been identified as inhibitors of serine proteinases, targeting chymotrypsin, elastase and trypsin. These inhibitors share 30-40% sequence identity with one another, but have virtually no sequence identity with members of any of the other families of serine proteinase inhibitors. The crystal structure of the complex of porcine pancreatic elastase with a chymotrypsin/elastase inhibitor from Ascaris suum (the C/E-1 inhibitor) has been solved to 2.4 A resolution by the molecular replacement method. The C/E-1 inhibitor exhibits a novel folding motif. There are only two small beta-sheets and two single-turn 3(10)-helices in this inhibitor. Unlike the majority of proteins, the C/E-1 inhibitor does not have a hydrophobic core. The presence and unique topography of the five disulfide bridges suggests that they play important roles in maintaining the tertiary structure of the inhibitor. In addition, the side chains of several charged residues from electrostatic and hydrogen-bonding cascades, which also probably compensate for the lack of extensive secondary structures and a hydrophobic core. The reactive-site loop of this inhibitor displays a conformation that is characteristic of most serine proteinase inhibitors. The structure of the C/E-1 inhibitor confirms that inhibitors from Ascaris suum belong to a novel family of proteinase inhibitors. It also provides conclusive evidence for the correct disulfide bridge connections. The C/E-1 inhibitor probably acts by a common inhibitory mechanism proposed for other substrate-like protein inhibitors of serine proteinases. The unusual molecular scaffolding presents a challenge to current folding algorithms. Proteins like the C/E-1 inhibitor may provide a valuable model system to study how the primary sequence of a protein dictates its three-dimensional structure.

  • Organizational Affiliation

    Department of Biochemistry, University of Alberta, Edmonton, Canada.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
A, B
240Sus scrofaMutation(s): 0 
Find proteins for P00772 (Sus scrofa)
Explore P00772 
Go to UniProtKB:  P00772
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP00772
Sequence Annotations
  • Reference Sequence
Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 2
MoleculeChains Sequence LengthOrganismDetailsImage
C, D
61Ascaris suumMutation(s): 0 
Find proteins for P07851 (Ascaris suum)
Explore P07851 
Go to UniProtKB:  P07851
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP07851
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 2.40 Å
  • Space Group: P 32 2 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 84.02α = 90
b = 84.02β = 90
c = 190.93γ = 120
Software Package:
Software NamePurpose
X-GENdata scaling
X-GENdata reduction

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 1999-04-05
    Type: Initial release
  • Version 1.1: 2007-10-16
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Derived calculations, Version format compliance
  • Version 1.3: 2017-10-04
    Changes: Refinement description
  • Version 1.4: 2023-08-09
    Changes: Data collection, Database references, Refinement description