Effect of phospholipid on trichosanthin adsorption at the air-water interface

Trichosanthin (TCS) is a toxic protein with multiple pharmacological properties. It belongs to the type I ribosome inactivating protein (RIP) family and can inactivate the eukaryotic ribosome through its RNA N-glycosidase activity. The interaction between TCS and phospholipid membrane was thought to be essential for its physiological effect, for it must get across the cell membrane before it can enter the cytoplasm and exert its RIP function. In order to study the TCS-phospholipid interaction, the difference between spontaneous and phospholipid induced adsorption of TCS at the air-water interface was investigated, and the results were analyzed according to the diffusion-penetration-rearrangement adsorption model. The results showed that both negatively charged 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) and neutral 1,2-dipalmitoyl-sn-glycero-3-phosphocholine can accelerate the adsorption rate, while there exists a possible membrane induced conformational change of TCS which is specific for the negatively charged DPPG. We also proposed a revised model for the diffusion controlled initial adsorption period.