Analysis of Intermedilysin in Human Specific Cytolytic Mechanism : Design and Application for Cell Targeting Module.

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Intermedilysin (ILY), a human specific cytolysin secreted by Streptococcus intermedius, is a member of the gene of SLO-family cytolysin (SFC), but differs by exhibiting a low affinity to cholesterol (CHL) in addition to human specificity. We modeled ILY molecule using perfringolysin O (PFO) X-ray data, and observed four domain (domain 1 〜 domain 4) in the molecule. From the analysis of ILY model, the domain 4 seems to be the human cell membrane associated region. Especially, extended-NTD sequence at ILY C-terminal appeared an important factor for human specific cytolysis. Indeed, the NTD-deleted ILY mutant (ΔNTD-ILY) decreased the hemolytic activity for human erythrocytes. Then we considered that the C-terminal NTD should be concerning with the cluster formation on the human cell membrane.Moreover we constructed the antiCEA-antibody conjugated ILY domain4 (antiCEA-ILY4D), and examined the cell delivery system. AntiCEA-ILY4D bind to human erythrocyte (ET) membrane easily, and this ET-AntiCEA-ILY4D module recognized CEA-positive TT cell. Now we are improving these targeting modules.