Emerin intermolecular links to emerin and BAF

Abstract

Emerin is a conserved nuclear membrane LEM-domain protein that binds lamins and BAF (barrier-to-integration factor; BANF1) as a component of nuclear lamina structure. We report an advance in understanding the molecular basis of emerin function: inter-molecular emerin-emerin association. Residues 170–220 were sufficient to bind other emerin molecules homotypically (via residues 170–220) or heterotypically in vitro. Deletion analysis showed residues 187–220 contain a positive element essential for intermolecular association in cells. Conversely, deletion of residues 168–186 inactivated a proposed negative element, required to limit or control association. GFP-emerin association with nuclear BAF in cells required the LEM-domain, and positive element. Emerin peptide arrays revealed direct binding of residues 170–220 to residues 206–225 (proposed positive element) and two ‘heterotypic’ partners: residues 147∼174 (particularly 153PMYGRDSAYQSITHYRP169) and the LEM-domain. Emerin residues 1–132 and 159–220 (159SAYQSITHYRPVS171 being important or essential)— were each sufficient to bind lamin A or B1 tails in vitro, identifying two independent regions of molecular contact with lamins. These results, and predicted emerin intrinsic disorder, support multiple ‘backbone’ and LEM-domain configurations of a proposed intermolecular emerin network at the nuclear envelope.