Structural and functional characterization of human Iba proteins

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Item Type:	Article
Title:	Structural and functional characterization of human Iba proteins
Creators Name:	Schulze, J.O., Quedenau, C., Roske, Y., Adam, T., Schueler, H., Behlke, J., Turnbull, A.P., Sievert, V., Scheich, C., Mueller, U., Heinemann, U. and Buessow, K.
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 Ca(2+). 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 Ca(2+). Furthermore, no binding of Ca(2+) up to 0.1 mm was detected by equilibrium dialysis. Correspondingly, Iba EF-hand motifs lack residues essential for strong Ca(2+) 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.
Keywords:	Actin Cross-Linking, Allograft Inflammatory Factor 1, Calcium Binding, EF-Hand, Ionized Calcium Binding Adapter Molecule, Actins, Amino Acid Sequence, Calcium-Binding Proteins, X-Ray Crystallography, DNA-Binding Proteins, Dimerization, Hela Cells, Microfilament Proteins, Molecular Models, Molecular Sequence Data, Sequence Alignment, Shigella
Source:	FEBS Journal
ISSN:	1742-464X
Publisher:	Wiley-Blackwell
Volume:	275
Number:	18
Page Range:	4627-4640
Date:	September 2008
Official Publication:	https://doi.org/10.1111/j.1742-4658.2008.06605.x
PubMed:	View item in PubMed

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