Simultaneous Formation of Right- and Left-handed Anti-parallel Coiled-coil Interfaces by a Coil2 Fragment of Human Lamin A Larisa E. Kapinos 1 ⁎, Peter Burkhard 2 , Harald Herrmann 3 , Ueli Aebi 1 and Sergei V. Strelkov 4 ⁎ 1 M.E. Müller Institute for Structural Biology, Biozentrum, University of Basel, Switzerland 2 Institute of Materials Science and Departement of Molecular and Cell Biology, University of Connecticut, USA 3 German Cancer Research Centre, Heidelberg, Germany 4 Department of Pharmaceutical Sciences, Katholieke Universiteit Leuven, Belgium Received 7 December 2010; received in revised form 15 February 2011; accepted 16 February 2011 Available online 24 February 2011 Edited by R. Huber Keywords: intermediate filaments; nuclear lamins; left-handed coiled coil; right-handed coiled coil; filament assembly The elementary building block of all intermediate filaments (IFs) is a dimer featuring a central α-helical rod domain flanked by the N- and C-terminal end domains. In nuclear IF proteins (lamins), the rod domain consists of two coiled-coil segments, coil1 and coil2, that are connected by a short non- helical linker. Coil1 and the C-terminal part of coil2 contain the two highly conserved IF consensus motifs involved in the longitudinal assembly of dimers. The previously solved crystal structure of a lamin A fragment (residues 305–387) corresponding to the second half of coil2 has yielded a parallel left-handed coiled coil. Here, we present the crystal structure and solution properties of another human lamin A fragment (residues 328–398), which is largely overlapping with fragment 305–387 but harbors a short segment of the tail domain. Unexpectedly, no parallel coiled coil forms within the crystal. Instead, the α-helices are arranged such that two anti- parallel coiled-coil interfaces are formed. The most significant interface has a right-handed geometry, which is accounted for by a characteristic 15-residue repeat pattern that overlays with the canonical heptad repeat pattern. The second interface is a left-handed anti-parallel coiled coil based on the predicted heptad repeat pattern. In solution, the fragment reveals only a weak dimerization propensity. We speculate that the C-terminus of coil2 might unzip, thereby allowing for a right-handed coiled-coil interface to form between two laterally aligned dimers. Such an interface might co-exist with a heterotetrameric left-handed coiled-coil assembly, which is expected to be responsible for the longitudinal A CN contact. © 2011 Elsevier Ltd. All rights reserved. Introduction The nuclear lamina, a structure observed closely attached to the inner nuclear membrane in all metazoan cells, is made from nuclear intermediate filament (IF) proteins; i.e. the lamins. 1 In humans, they are encoded by genes LMNA, LMNB1 and LMNB2 and most cells contain all three of them, although in varying proportions. 2 In contrast, cytoplasmic IF proteins are generated in a cell *Corresponding authors. E-mail addresses: larisa.kapinos@unibas.ch; sergei.strelkov@pharm.kuleuven.be. Abbreviations used: IF, intermediate filaments; IFCM, intermediate filament consensus motif; PDB, Protein Data Bank; RMSD, root-mean-square deviation; SAD, single-wavelength anomalous dispersion; NCS, non-crystallographic symmetry; DM, density modification. doi:10.1016/j.jmb.2011.02.037 J. Mol. Biol. (2011) 408, 135–146 Contents lists available at www.sciencedirect.com Journal of Molecular Biology journal homepage: http://ees.elsevier.com.jmb 0022-2836/$ - see front matter © 2011 Elsevier Ltd. All rights reserved.