Nuclear lamin proteins: common structures for paracrystalline, filamentous and lattice forms

It is shown that the packing of the lamination molecules in both the in vivo and the in vitro assemblies can be explained in terms of a single model in which arrays of antiparallel lamin molecules are half-staggered with respect to one another.

Abstract

Nuclear lamins isolated from a variety of sources and classified as Type V intermediate filament (IF) proteins form a variety of closely related filamentous or paracrystalline polymorphs. Furthermore, the nuclear lamina observed in Xenopus oocytes was shown to consist of an approximately orthogonal lattice of filaments. All of the structures observed thus far have axial periodicities of about 25 or 50 nm. In this work it is shown that the packing of the lamin molecules in both the in vivo and the in vitro assemblies can be explained in terms of a single model in which arrays of antiparallel lamin molecules are half-staggered with respect to one another. Such a scheme closely resembles that previously proposed for four-chain complexes in Types I–IV IF proteins. Higher levels of structure, however, differ significantly. A key interaction in the models of the various lamin assemblies is one occurring between similarly directed segments encompassing the highly conserved part of segment IA and that at the C-terminal end of segment 2B. Such an interaction may also prove to be of importance in IF structure.