Apo and Calcium-Bound Crystal Structures of Cytoskeletal Protein Alpha-14 Giardin (Annexin E1) from the Intestinal Protozoan Parasite Giardia lamblia
2009 (English)In: Journal of Molecular Biology, ISSN 0022-2836, E-ISSN 1089-8638, Vol. 385, no 4, 1098-1112 p.Article in journal (Refereed) Published
Alpha-14 giardin (annexin E1), a member of the alpha giardin family of annexins, has been shown to localize to the flagella of the intestinal protozoan parasite Giardia lamblia. Alpha giardins show a common ancestry with the annexins, a family of proteins most of which bind to phospholipids and cellular membranes in a Ca2+-dependent manner and are implicated in numerous membrane-related processes including cytoskeletal rearrangements and membrane organization. It has been proposed that alpha-14 giardin may play a significant role during the cytoskeletal rearrangement during differentiation of Giardia. To gain a better understanding of alpha-14 giardin's mode of action and its biological role, we have determined the three-dimensional structure of alpha-14 giardin and its phospholipid-binding properties. Here, we report the apo crystal structure of 2 alpha-14 giardin determined in two different crystal forms as well as the Ca2+-bound crystal structure of alpha-14 giardin, refined to 1.9, 1.6 and 1.65 angstrom, respectively. Although the overall fold of alpha-14 giardin is similar to that of alpha-11 giardin, multiwavelength anomalous dispersion phasing was required to solve the alpha-14 giardin structure, indicating significant structural differences between these two members of the alpha giardin family. Unlike most annexin structures, which typically possess N-terminal domains, alpha-14 giardin is composed of only a core domain, followed by a C-terminal extension that may serve as a ligand for binding to cytoskeletal protein partners in Giardia. In the Ca2+-bound structure we detected five bound calcium ions, one of which is a novel, highly coordinated calcium-binding site not previously observed in annexin structures. This novel high-affinity calcium-binding site is composed of seven protein donor groups, a feature rarely observed in crystal structures. In addition, phospholipid-binding assays suggest that alpha-14 giardin exhibits calcium-dependent binding to phospholipids that coordinate cytoskeletal disassembly/assembly during differentiation of the parasite.
Place, publisher, year, edition, pages
2009. Vol. 385, no 4, 1098-1112 p.
Giardia, annexin, calcium binding, flagella, cytoskeleton
IdentifiersURN: urn:nbn:se:uu:diva-137339DOI: 10.1016/j.jmb.2008.11.012ISI: 000263073400008OAI: oai:DiVA.org:uu-137339DiVA: diva2:378260