Isolation and Characterization of Okadaic Acid Binding Proteins from the Marine Sponge Halichondria okadai

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• 作者：Naoyuki Sugiyama ; Keiichi Konoki ; Kazuo Tachibana
• 刊名：Biochemistry
• 出版年：2007
• 出版时间：October 9, 2007
• 年：2007
• 卷：46
• 期：40
• 页码：11410 - 11420
• 全文大小：417K
• 年卷期：v.46,no.40(October 9, 2007)
• ISSN：1520-4995

文摘

Okadaic acid, first isolated from the marine sponge Halichondria okadai, is a potent inhibitorof protein phosphatases 1 and 2A (PP1 and PP2A, respectively). Photoaffinity labeling experimentspreviously performed with biotinylated photoreactive okadaic acid revealed the presence of okadaic acidbinding protein (OABP) in the crude extract of H. okadai. In this article, OABP1 and OABP2 werepurified from H. okadai as guided by the binding affinity of [27-³H]okadaic acid. OABP1 has anapproximate molecular mass of 37 kDa in SDS-PAGE analysis. Edman degradation followed by molecularcloning and sequencing identified OABP1 as being 88% identical to the rabbit PP2A catalytic subunit.On the other hand, HPLC analysis revealed that OABP2 consists of three 22 kDa proteins (OABP2.1,OABP2.2, and OABP2.3). Electrospray ionization mass spectrometry indicated that OABP2.1 and OABP2.2form a complex with okadaic acid. The complete amino acid sequence of OABP2, determined by Edmandegradation and molecular cloning, showed that OABP2.1 is 96% identical to OABP2.2 and 66% identicalto OABP2.3, while being very slightly homologous to any protein phosphatases known to date. OABP2did not exhibit phosphatase activity, though it bound to okadaic acid with a K_d of 0.97 nM. Furthermore,OABP2 was not detected in the sponge Halichondria japonica or the dinoflagellate Prorocentrum lima.We thus speculated that OABP2 might be involved in detoxifying okadaic acid.