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- Title
Structural and functional characterization of human Iba proteins.
- Authors
Schulze, Jörg O.; Quedenau, Claudia; Roske, Yvette; Adam, Thomas; Schüler, Herwig; Behlke, Joachim; Turnbull, Andrew P.; Sievert, Volker; Scheich, Christoph; Mueller, Uwe; Heinemann, Udo; Büssow, Konrad
- Abstract
Iba2 is a homolog of ionized calcium-binding adapter molecule 1 (Iba1), a 17-kDa protein that binds and cross-links filamentous actin (F-actin) and localizes to membrane ruffles and phagocytic cups. Here, we present the crystal structure of human Iba2 and its homodimerization properties, F-actin cross-linking activity, cellular localization and recruitment upon bacterial invasion in comparison with Iba1. The Iba2 structure comprises two central EF-hand motifs lacking bound Ca2+. Iba2 crystallized as a homodimer stabilized by a disulfide bridge and zinc ions. Analytical ultracentrifugation revealed a different mode of dimerization under reducing conditions that was independent of Ca2+. Furthermore, no binding of Ca2+ up to 0.1 mm was detected by equilibrium dialysis. Correspondingly, Iba EF-hand motifs lack residues essential for strong Ca2+ coordination. Sedimentation experiments and microscopy detected pronounced, indistinguishable F-actin binding and cross-linking activity of Iba1 and Iba2 with induction of F-actin bundles. Fluorescent Iba fusion proteins were expressed in HeLa cells and co-localized with F-actin. Iba1 was recruited into cellular projections to a larger extent than Iba2. Additionally, we studied Iba recruitment in a Shigella invasion model that induces cytoskeletal rearrangements. Both proteins were recruited into the bacterial invasion zone and Iba1 was again concentrated slightly higher in the cellular extensions.
- Subjects
MOLECULES; PHAGOCYTOSIS; PROTEINS; CALCIUM-binding proteins; ACTIN
- Publication
FEBS Journal, 2008, Vol 275, Issue 18, p4627
- ISSN
1742-464X
- Publication type
Article
- DOI
10.1111/j.1742-4658.2008.06605.x