Binding of diarrheic shellfish poisoning toxins to okadaic acid binding proteins purified from the sponge Halichondria okadai |
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Authors: | Keiichi Konoki Kaori Saito Hiroki Matsuura Naoyuki Sugiyama Yuko Cho Mari Yotsu-Yamashita Kazuo Tachibana |
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Institution: | 1. Graduate School of Agricultural Science, Tohoku University, Tsutsumidori-Amamiyamachi 1-1, Aoba-ku, Sendai 981-8555, Japan;2. Department of Chemistry, School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan |
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Abstract: | Okadaic acid (OA) and dinophysistoxin-1 (DTX1) cause diarrheic shellfish poisoning. This article examines the biochemical interactions of the two toxins with novel okadaic acid binding proteins (OABPs) 2.1 and 2.3, originally isolated from the marine sponge Halichondria okadai. First, recombinant OABPs 2.1 and 2.3 were expressed in Escherichia coli BL21 (DE3) cells. Binding assays using 24-3H]OA and the recombinant OABP 2.1 or 2.3 demonstrated the dissociation constant Kd of 1.30 ± 0.56 nM and 1.54 ± 0.35 nM, respectively. Binding of 24-3H]okadaic acid to recombinant OABP2.1 was almost equally replaced with OA and DTX1. OA-induced cytotoxicity in mouse leukemia P388 cells was inhibited in the presence of the recombinant OABPs 2.1 and 2.3 with an EC50 of 92 ± 8.4 nM and 87 ± 13 nM, respectively. These results suggest that the blockage of OA-induced cytotoxicity by OABPs 2.1 and 2.3 may be involved in regulating symbiotic relationships present in the sponge H. okadai. |
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