Maynes J T, Bateman K S, Cherney M M, Das A K, Luu H A, Holmes C F, James M N
Canadian Institutes of Health Research, Group in Protein Structure and Function, Department of Biochemistry, Faculty of Medicine, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
J Biol Chem. 2001 Nov 23;276(47):44078-82. doi: 10.1074/jbc.M107656200. Epub 2001 Sep 4.
Protein phosphatase-1 (PP1) plays a key role in dephosphorylation in numerous biological processes such as glycogen metabolism, cell cycle regulation, smooth muscle contraction, and protein synthesis. Microorganisms produce a variety of inhibitors of PP1, which include the microcystin class of inhibitors and okadaic acid, the latter being the major cause of diarrhetic shellfish poisoning and a powerful tumor promoter. We have determined the crystal structure of the molecular complex of okadaic acid bound to PP1 to a resolution of 1.9 A. This structure reveals that the acid binds in a hydrophobic groove adjacent to the active site of the protein and interacts with basic residues within the active site. Okadaic acid exhibits a cyclic structure, which is maintained via an intramolecular hydrogen bond. This is reminiscent of other macrocyclic protein phosphatase inhibitors. The inhibitor-bound enzyme shows very little conformational change when compared with two other PP1 structures, except in the inhibitor-sensitive beta12-beta13 loop region. The selectivity of okadaic acid for protein phosphatases-1 and -2A but not PP-2B (calcineurin) may be reassessed in light of this study.
蛋白磷酸酶-1（PP1）在众多生物过程的去磷酸化中发挥关键作用，如糖原代谢、细胞周期调控、平滑肌收缩和蛋白质合成。微生物产生多种PP1抑制剂，包括微囊藻毒素类抑制剂和冈田酸，后者是腹泻性贝类中毒的主要原因，也是一种强大的肿瘤促进剂。我们已确定与PP1结合的冈田酸分子复合物的晶体结构，分辨率为1.9埃。该结构表明，该酸结合在蛋白质活性位点附近的疏水凹槽中，并与活性位点内的碱性残基相互作用。冈田酸呈现出一种环状结构，通过分子内氢键得以维持。这让人联想到其他大环蛋白磷酸酶抑制剂。与其他两种PP1结构相比，除了抑制剂敏感的β12-β13环区域外，结合抑制剂的酶显示出很少的构象变化。鉴于这项研究，可能需要重新评估冈田酸对蛋白磷酸酶-1和-2A而非PP-2B（钙调神经磷酸酶）的选择性。
