Crystal Structure of Alpha-11 Giardin

Experimental Data Snapshot

  • Resolution: 1.10 Å
  • R-Value Free: 0.225 
  • R-Value Work: 0.195 
  • R-Value Observed: 0.196 

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Apo and Calcium-bound Crystal Structures of Alpha-11 Giardin, an Unusual Annexin from Giardia lamblia

Pathuri, P.Nguyen, E.T.Svard, S.G.Luecke, H.

(2007) J Mol Biol 368: 493-508

  • DOI: https://doi.org/10.1016/j.jmb.2007.02.016
  • Primary Citation of Related Structures:  
    2II2, 2IIC

  • PubMed Abstract: 

    Alpha-11 giardin is a member of the multi-gene alpha-giardin family in the intestinal protozoan, Giardia lamblia. This gene family shares an ancestry with the annexin super family, whose common characteristic is calcium-dependent binding to membranes that contain acidic phospholipids. Several alpha giardins are highly expressed during parasite-induced diarrhea in humans. Despite being a member of a large family of proteins, little is known about the function and cellular localization of alpha-11 giardin, although giardins are often associated with the cytoskeleton. It has been shown that Giardia exhibits high levels of alpha-11 giardin mRNA transcript throughout its life cycle; however, constitutive over-expression of this protein is lethal to the parasite. Determining the three-dimensional structure of an alpha-giardin is essential to identifying functional domains shared in the alpha-giardin family. Here we report the crystal structures of the apo and Ca(2+)-bound forms of alpha-11 giardin, the first alpha giardin to be characterized structurally. Crystals of apo and Ca(2+)-bound alpha-11 giardin diffracted to 1.1 A and 2.93 A, respectively. The crystal structure of selenium-substituted apo alpha-11 giardin reveals a planar array of four tandem repeats of predominantly alpha-helical domains, reminiscent of previously determined annexin structures, making this the highest-resolution structure of an annexin to date. The apo alpha-11 giardin structure also reveals a hydrophobic core formed between repeats I/IV and II/III, a region typically hydrophilic in other annexins. Surprisingly, the Ca(2+)-bound structure contains only a single calcium ion, located in the DE loop of repeat I and coordinated differently from the two types of calcium sites observed in previous annexin structures. The apo and Ca(2+)-bound alpha-11 giardin structures assume overall similar conformations; however, Ca(2+)-bound alpha-11 giardin crystallized in a lower-symmetry space group with four molecules in the asymmetric unit. Vesicle-binding studies suggest that alpha-11 giardin, unlike most other annexins, does not bind to vesicles composed of acidic phospholipids in a calcium-dependent manner.

  • Organizational Affiliation

    Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697, USA.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Alpha-11 giardin310Giardia intestinalisMutation(s): 0 
Find proteins for Q4VPP2 (Giardia intestinalis)
Explore Q4VPP2 
Go to UniProtKB:  Q4VPP2
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ4VPP2
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 1.10 Å
  • R-Value Free: 0.225 
  • R-Value Work: 0.195 
  • R-Value Observed: 0.196 
  • Space Group: P 21 21 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 45.951α = 90
b = 60.954β = 90
c = 119.909γ = 90
Software Package:
Software NamePurpose
d*TREKdata scaling
PDB_EXTRACTdata extraction
ADSCdata collection
HKL-2000data reduction

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2007-04-17
    Type: Initial release
  • Version 1.1: 2008-05-01
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Version format compliance
  • Version 1.3: 2024-02-21
    Changes: Data collection, Database references, Derived calculations