Resonance assignments and secondary structure of a phytocystatin from Sesamum indicum

A cDNA encoding a cysteine protease inhibitor, cystatin was cloned from sesame (Sesamum indicum L.) seed. This clone was constructed into an expression vector and expressed in E. coli and purified to homogeneous. The recombinant sesame cystatin (SiCYS) showed effectively inhibitory activity toward C1 cysteine proteases. In order to unravel its inhibitory action from structural point of view, multidimensional heteronuclear NMR techniques were used to characterize the structure of SiCYS. The full ¹H, ¹⁵N, and ¹³C resonances of SiCYS were assigned. The secondary structure of SiCYS was identified by using the assigned chemical shifts of ¹H^α, ¹³C^α, ¹³C^β, and ¹³CO through the consensus chemical shift index (CSI). The results of CSI analysis of SiCYS suggest eight β-strands (residues 33–46, 51–61, 63–75, 80–87, 150–155, 157–169, 172–183, and 192–195) and two α-helices (residues 16–30, and 120–135).