The Carboxyl-Terminal Region Common to Lamins A and C Contains a DNA Binding Domain

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Abstract
Lamins A and C are intermediate filament proteins which polymerize into the nucleus to form the nuclear lamina network. The lamina is apposed to the inner nuclear membrane and functions in tethering chromatin to the nuclear envelope and in maintaining nuclear shape. We have recently characterized a globular domain that adopts an immunoglobulin fold in the carboxyl-terminal tail common to lamins A and C. Using an electrophoretic mobility shift assay (EMSA), we show that a peptide containing this domain interacts in vitro with DNA after dimerization through a disulfide bond, but does not interact with the core particle or the dinucleosome. The covalent dimer binds a 30−40 bp DNA fragment with a micromolar affinity and no sequence specificity. Using nuclear magnetic resonance (NMR) and an EMSA, we observed that two peptide regions participate in the DNA binding: the unstructured amino-terminal part containing the nuclear localization signal and a large positively charged region centered around amino acid R482 at the surface of the immunoglobulin-like domain. Mutations R482Q and -W, which are responsible for Dunnigan-type partial lipodystrophy, lower the affinity of the peptide for DNA. We conclude that the carboxyl-terminal end of lamins A and C binds DNA and suggest that alterations in lamin−DNA interactions may play a role in the pathophysiology of some lamin-linked diseases.