The N terminal domain of Siah interacting protein (SIP) adopts a helical hairpin structure with a hydrophobic core stabilised by a classic knobs-and-holes arrangement of side chains contributed by the two amphipathic helices. Little is known about this domain's function, except that it is crucial for interactions with Siah. It has also been hypothesised that SIP can dimerise through this N terminal domain [1].

1: The modular structure of SIP facilitates its role in stabilizing multiprotein assemblies. Bhattacharya S, Lee YT, Michowski W, Jastrzebska B, Filipek A, Kuznicki J, Chazin WJ; Biochemistry. 2005;44:9462-9471. PMID:15996101