PMID: 21059355

Authors:

Garcia-Saez I, Lacroix FB, Blot D, Gabel F, Skoufias DA

Title:

Structural characterization of HBXIP: the protein that interacts with the anti-apoptotic protein survivin and the oncogenic viral protein HBx.

Journal:

J Mol Biol. 2011 Jan 14;405(2):331-40. Epub 2010 Nov 6.

Abstract:

Hepatitis B X-interacting protein (HBXIP) is a ubiquitous protein that was originally identified as a binding partner of the hepatitis B viral protein HBx. HBXIP is also thought to serve as an anti-apoptotic cofactor of survivin, promoting the suppression of pro-caspase-9 activation. Here were port the crystal structure of the shortest isoform of HBXIP (91 aa long, approximately 11 kDa) at 1.5 A resolution. HBXIP crystal shows a monomer per asymmetric unit, with a profilin-like fold which is common to a super family of proteins, the Roadblock/LC7 domain family involved in protein-protein interactions. Based on this fold, we propose that HBXIP can form a dimer that can indeed be found in the crystal when symmetric molecules are generated around the asymmetric unit. This dimer shows an extended beta-sheet area formed by 10 anti-parallel beta-strands from both subunits. Another interesting aspect of the proposed HBXIP dimer interface is the presence of a small leucine zipper between the two alpha2 helices of each monomer. In solution, the scattering curve obtained by small-angle X-ray scattering for the sample used for crystallization indicates that the protein is dimeric form in solution. The fit between the experimental small angle X-ray scattering curve and the back calculated curves for two potential crystal dimers shows a significant preference for the Roadblock/LC7 fold dimer model. Moreover, the HBXIP crystal structure represents a step towards understanding the cellular role of HBXIP.