1.C.100 The Thermostable Direct Hemolysin (TDH) Family Thermostable direct hemolysin (TDH) is a major virulence factor of Vibrio parahaemolyticus that causes pandemic foodborne enterocolitis mediated by seafood. TDH is a tetramer in solution and possesses extreme hemolytic activity. Yanagihara et al. (2010) presented the crystal structure of the TDH tetramer at 1.5 A resolution. It forms a central pore with dimensions of 23 A in diameter and approximately 50 A in depth. Pi-cation interactions between protomers comprising the tetramer were indispensable for hemolytic activity. The N-terminal region was intrinsically disordered outside of the pore. Molecular dynamic simulations suggested that water molecules permeate freely through the central and side channel pores. Electron micrographs showed that TDH attached to liposomes. These findings imply a novel membrane attachment mechanism by a soluble tetrameric pore-forming toxin. TDH and TDH-related hemolysin (TRH) are major virulence factors of Vibrio parahaemolyticus. The crystal structure of the TDH tetramer with a central channel is known. Ohnishi et al. (2011) described the biophysical properties of TRH, which displays 67% amino acid similarity with TDH. Molecular modeling provided a good fit of the overall structure of TDH and TRH. TRH formed tetramer in solution. These toxins showed hemolytic activity on red blood cells. Their 3-d structures reveal a β-sandwich domain similar to actinoporins plus a C-terminal region linked to the barrel via a disulfide bond (Kundu et al. 2016).
References:
Chen, X., M. Duan, Y. Chang, M. Ye, Z. Wang, S. Wu, and N. Duan. (2024). Assembly of a multivalent aptamer for efficient inhibition of thermostable direct hemolysin toxicity induced by Vibrio parahaemolyticus. J Hazard Mater 478: 135452.
Huntley, J.S. and A.C. Hall. (1994). Aspects of the haemolytic reaction induced by Kanagawa haemolysin of Vibrio parahaemolyticus. Toxicon 32: 1397-1412.
Kundu, N., S. Tichkule, S.B. Pandit, and K. Chattopadhyay. (2016). Disulphide Bond Restrains C-Terminal Region of Thermostable Direct Hemolysin during Folding to Promote Oligomerization. Biochem. J. [Epub: Ahead of Print]
Ohnishi, K., K. Nakahira, S. Unzai, K. Mayanagi, H. Hashimoto, K. Shiraki, T. Honda, and I. Yanagihara. (2011). Relationship between heat-induced fibrillogenicity and hemolytic activity of thermostable direct hemolysin and a related hemolysin of Vibrio parahaemolyticus. FEMS Microbiol. Lett. 318: 10-17.
Yanagihara, I., K. Nakahira, T. Yamane, S. Kaieda, K. Mayanagi, D. Hamada, T. Fukui, K. Ohnishi, S. Kajiyama, T. Shimizu, M. Sato, T. Ikegami, M. Ikeguchi, T. Honda, and H. Hashimoto. (2010). Structure and functional characterization of Vibrio parahaemolyticus thermostable direct hemolysin. J. Biol. Chem. 285: 16267-16274.
Examples:
TC#	Name	Organismal Type	Example
1.C.100.1.1	Thermostable direct hemolysin or Kanagawa haemolysin, TDH, Tdh2, trh of 189 aas. It exhibits monovalent cation selectivity in the order: Cs⁺ > Li⁺ > K⁺ > Rb⁺ > Na⁺, confirming that TDH is the important leak-inducing agent (Huntley and Hall 1994). The crystal structure is known (3A57_A); Ohnishi et al., 2011). Assembly of a multivalent aptamer efficiently inhibits the thermostable direct hemolysin toxicity induced by Vibrio parahaemolyticus (Chen et al. 2024).	Bacteria	*TDH of Vibrio parahaemolyticus* (B3IW71)**

1.C.100.1.2	*TDH-related hemolysin, TRH (67% similarity to TDH (Ohnishi et al., 2011))*	Bacteria	*TRH of Vibrio parahaemolyticus* (Q5DMU5)**

1.C.100.1.3	Thermostable direct hemolysin-family toxin,TDH. partial, 151 aa		TDH of Vibrio cholerae