The L27_2 domain is a protein-protein interaction domain capable of organising scaffold proteins into supramolecular assemblies by formation of heteromeric L27_2 domain complexes. L27_2 domain-mediated protein assemblies have been shown to play essential roles in cellular processes including asymmetric cell division, establishment and maintenance of cell polarity, and clustering of receptors and ion channels. Members of this family form specific heterotetrameric complexes, in which each domain contains three alpha-helices. The two N-terminal helices of each L27_2 domain pack together to form a tight, four-helix bundle in the heterodimer, whilst the third helix of each L27_2 domain forms another four-helix bundle that assembles the two units of the heterodimer into a tetramer [1].

1: A unified assembly mode revealed by the structures of tetrameric L27 domain complexes formed by mLin-2/mLin-7 and Patj/Pals1 scaffold proteins. Feng W, Long JF, Zhang M; Proc Natl Acad Sci U S A. 2005;102:6861-6866. PMID:15863617