title: Characterization of the head-to-tail overlap complexes formed by human lamin A, B1 and B2 "half-minilamin" dimers.
abstract: Half-minilamins, representing amino- and carboxy-terminal fragments of human lamins A, B1 and B2 with a truncated central rod domain, were investigated for their ability to form distinct head-to-tail-type dimer complexes. This mode of interaction represents an essential step in the longitudinal assembly reaction exhibited by full-length lamin dimers. As determined by analytical ultracentrifugation, the amino-terminal fragments were soluble under low ionic strength conditions sedimenting with distinct profiles and s-values (1.6-1.8 S) indicating the formation of coiled-coil dimers. The smaller carboxy-terminal fragments were, except for lamin B2, largely insoluble under these conditions. However, after equimolar amounts of homotypic amino- and carboxy-terminal lamin fragments had been mixed in 4 M urea, upon subsequent renaturation the carboxy-terminal fragments were completely rescued from precipitation and distinct soluble complexes with higher s-values (2.3-2.7 S) were obtained. From this behavior, we conclude that the amino- and carboxy-terminal coiled-coil dimers interact to form distinct oligomers (i.e. tetramers). Furthermore, a corresponding interaction occurred also between heterotypic pairs of A- and B-type lamin fragments. Hence, A-type lamin dimers may interact with B-type lamin dimers head-to-tail to yield linear polymers. These findings indicate that a lamin dimer principally has the freedom for a "combinatorial" head-to-tail association with all types of lamins, a property that might be of significant importance for the assembly of the nuclear lamina. Furthermore, we suggest that the head-to-tail interaction of the rod end domains represents a principal step in the assembly of cytoplasmic intermediate filament proteins too.
authors.affiliation: M.E. Müller Institute for Structural Biology, Biozentrum, University of Basel, CH-4056 Basel, Switzerland.
authors.forename: Larisa E
authors.initials: LE
authors.lastname: Kapinos
authors.forename: Jens
authors.initials: J
authors.lastname: Schumacher
authors.forename: Norbert
authors.initials: N
authors.lastname: Mücke
authors.forename: Gia
authors.initials: G
authors.lastname: Machaidze
authors.forename: Peter
authors.initials: P
authors.lastname: Burkhard
authors.forename: Ueli
authors.initials: U
authors.lastname: Aebi
authors.forename: Sergei V
authors.initials: SV
authors.lastname: Strelkov
authors.forename: Harald
authors.initials: H
authors.lastname: Herrmann
mesh_terms: D000595:Amino Acid Sequence; D006801:Humans; D034904:Lamin Type A / Q000737:chemistry / Q000378:metabolism*; D034921:Lamin Type B / Q000737:chemistry / Q000378:metabolism*; D008956:Models, Chemical; D008958:Models, Molecular; D025941:Protein Interaction Mapping; D055503:Protein Multimerization; D016415:Sequence Alignment; D012995:Solubility; D014461:Ultracentrifugation
chemical_list: D034904:Lamin Type A; D034921:Lamin Type B