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Apo and calcium-bound crystal structures of alpha-11 giardin, an unusual annexin from Giardia lamblia
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology.
2007 (English)In: Journal of Molecular Biology, ISSN 0022-2836, E-ISSN 1089-8638, Vol. 368, no 2, 493-508 p.Article in journal (Refereed) Published
Abstract [en]

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 througho ut 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 Ca2+- bound forms of alpha-11 giardin, the first alpha giardin to be characterized structurally. Crystals of apo and Ca2+ -bound alpha-11 giardin diffracted to d 1.1 angstrom and 2.93 angstrom, respectively. The crystal structure of selenium-substitute 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 Ca2+-bound structure contains only a single calcium ion, located in the DE loop of repeat I and calcium sites observed in coordinated differently from the two types of 2 previous annexin structures. The apo and Ca2+-bound alpha-11 giardin structures assume overall similar conformations; however, Ca2+-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.

Place, publisher, year, edition, pages
2007. Vol. 368, no 2, 493-508 p.
Keyword [en]
Giardia, annexin, intestinal protozoan, calcium-binding, cytoskeleton
National Category
Biological Sciences
URN: urn:nbn:se:uu:diva-144707DOI: 10.1016/j.jmb.2007.02.016ISI: 000245897400018PubMedID: 17355882OAI: oai:DiVA.org:uu-144707DiVA: diva2:394297
Available from: 2011-02-02 Created: 2011-02-02 Last updated: 2011-02-02Bibliographically approved

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