Structural characterization of PPTI, a kunitz-type protein from the venom of Pseudocerastes persicus.

The main purpose of this report is to investigate the structural property and new potential function of PPTI (Pseudocerastes Persicus Trypsin Inhibitor), a kunitz-type protein with inhibitory effect against trypsin proteolytic activity. Besides kunitz-type serine protease inhibitors, PPTI shows clear-cut similarities with dendrotoxins (DTXs), the other kunitz-type protein subfamily. The most important reason is the presence of functionally important residues of DTXs at correspondingly the same positions in PPTI. As such, we proposed the new ability of PPTI for inhibiting voltage-gated potassium channels and consequently its dual functionality. At first, we determined the solution structure of PPTI via Nuclear Magnetic Resonance (NMR) spectroscopy. Then by homology modeling, we constructed the model structure of trypsin-PPTI complex to confirm the same interaction pattern as trypsin-BPTI at complex interface. Finally, by Brownian dynamics (BD) simulations of PPTI NMR derived ensemble structure as ligand against homology model of human Kv1.1 potassium channel as receptor, we evaluated the potential DTX-like activity of PPTI. The results of our study support the proposed dual functionality of PPTI.