The L27_N domain plays a role in the biogenesis of tight junctions and in the establishment of cell polarity in epithelial cells. Each L27_N domain consists of three alpha-helices, the first two of which form an antiparallel coiled-coil. Two L27 domains come together to form a four-helical bundle with the antiparallel coiled-coils formed by the first two helices. The third helix of each domain forms another coiled-coil packing at one end of the four-helix bundle, creating a large hydrophobic interface: the hydrophobic interactions are the major force that drives heterodimer formation [1].

1: Structural basis for L27 domain-mediated assembly of signaling and cell polarity complexes. Li Y, Karnak D, Demeler B, Margolis B, Lavie A; EMBO J. 2004;23:2723-2733. PMID:15241471