Interactions between coiled-coil proteins: Drosophila lamin Dm0 binds to the bicaudal-D protein.

In a yeast two-hybrid screen we identified an interaction between Drosophila lamin Dm0, a structural nuclear protein, and BICD, a protein involved in oocyte development. The interaction can be reconstituted in vitro and takes place between segments of both proteins predicted to form coiled coils. The affinity for lamin Dm0 of the minimal binding site on BICD is modulated in a complex fashion by other BICD segments. A point mutation, F684I, that causes the dominant, bicaudal, Bic-D phenotype inhibits lamin binding in the context of the minimal lamin-binding site, but not in a larger BICD fragment. The minimal lamin-binding site of BICD binds to a few other coiled-coil proteins, but binding to these proteins is not influenced by the F684I point mutation, suggesting that the interaction with lamin may play a role in Bic-D function. Our structural studies demonstrated that BICD is 60-70% alpha-helical, is a dimer, and consists of two parts: a thin rod-shaped part of about 32 nm, and a thicker rod-shaped part of about 26 nm. Likely, the thinner rod-shaped part of full-length BICD consists of the N-terminal half of the protein, and the lamin-binding site is located within the thicker rod-shaped part.