Mad1 (6-21) is the 6-21 fragment of Mad1 protein. Mad1 (6-21) binds to mammalian Sin3A PAH2 with a Kd of ~29 nM[1].
The PAH2 domain of mSin3A adopts a left-handed, up-and-down, four-helix bundle structure with residues in all four helices as well as in the turn regions defining a compact structural domain with an extensive drophobic core. Helices α1 and α2 form a deep drophobic pocket, which constitutes the primary interaction surface for the Mad1 (6-21) peptide. The Mad1 (6-21) forms an amphipathic α helix in the complex and interacts with PAH2 mainly through the apolar surface of the helix[1].
[1]. K Brubaker, et al. Solution structure of the interacting domains of the Mad-Sin3 complex: implications for recruitment of a chromatin-modifying complex. Cell. 2000 Nov 10;103(4):655-65.