Mad1 (6-21) is a peptide fragment derived from the Mad1 protein, specifically encompassing residues 6 to 21. This fragment exhibits binding affinity towards the mammalian Sin3A PAH2 domain, with a Kd value of approximately 29 nM.

The PAH2 domain of mSin3A forms a left-handed, four-helix bundle with residues from all helices and turn regions creating a compact domain featuring a significant hydrophobic core. Helices α1 and α2 generate a deep hydrophobic pocket, serving as the main interaction site for the Mad1 (6-21) peptide. This Mad1 (6-21) peptide assumes an amphipathic α-helical structure upon binding, predominantly engaging with PAH2 through its nonpolar surface[1].