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Title: Structure of the N-terminal domain of the protein Expansion: an ‘Expansion’ to the Smad MH2 fold

Expansion is a modular protein that is conserved in protostomes. The first structure of the N-terminal domain of Expansion has been determined at 1.6 Å resolution and the new Nα-MH2 domain was found to belong to the Smad/FHA superfamily of structures. Gene-expression changes observed in Drosophila embryos after inducing the transcription factor Tramtrack led to the identification of the protein Expansion. Expansion contains an N-terminal domain similar in sequence to the MH2 domain characteristic of Smad proteins, which are the central mediators of the effects of the TGF-β signalling pathway. Apart from Smads and Expansion, no other type of protein belonging to the known kingdoms of life contains MH2 domains. To compare the Expansion and Smad MH2 domains, the crystal structure of the Expansion domain was determined at 1.6 Å resolution, the first structure of a non-Smad MH2 domain to be characterized to date. The structure displays the main features of the canonical MH2 fold with two main differences: the addition of an α-helical region and the remodelling of a protein-interaction site that is conserved in the MH2 domain of Smads. Owing to these differences, to the new domain was referred to as Nα-MH2. Despite the presence of the Nα-MH2more » domain, Expansion does not participate in TGF-β signalling; instead, it is required for other activities specific to the protostome phyla. Based on the structural similarities to the MH2 fold, it is proposed that the Nα-MH2 domain should be classified as a new member of the Smad/FHA superfamily.« less
;  [1] ;  [2] ;  [3] ;  [1] ;  [4] ;  [1] ;  [4] ;  [1] ;  [5]
  1. Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, 08028 Barcelona (Spain)
  2. Institut de Biologia Molecular de Barcelona, IBMB–CSIC, Baldiri Reixac 10, 08028 Barcelona (Spain)
  3. ALBA Synchrotron, BP 1413, km 3.3, Cerdanyola del Vallès (Spain)
  4. (Spain)
  5. (ICREA), Passeig Lluís Companys 23, 08010 Barcelona (Spain)
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Journal Article
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Journal Name: Acta Crystallographica. Section D: Biological Crystallography; Journal Volume: 71; Journal Issue: Pt 4; Other Information: PMCID: PMC4388265; PMID: 25849395; PUBLISHER-ID: kw5112; OAI:; Copyright (c) Beich-Frandsen et al. 2015; This is an open-access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.; Country of input: International Atomic Energy Agency (IAEA)
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