Gupta R P, Abou-Donia M B
Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina, 27708, USA.
Arch Biochem Biophys. 1999 May 15;365(2):268-78. doi: 10.1006/abbi.1999.1165.
Diisopropyl phosphorofluoridate (DFP) produces organophosphorus ester-induced delayed neurotoxicity (OPIDN) in hen, human, and other sensitive species. This is characterized by mild ataxia, which progresses to severe ataxia or paralysis in a few days. Ultrastructurally, OPIDN is associated with the degeneration of axons in central and peripheral nervous systems. Bacterially expressed longest human tau protein (htau40) phosphorylated by DFP-treated hen brain supernatant showed a decrease in microtubule binding in a shorter time than that phosphorylated by control hen brain supernatant. The decrease in htau40-microtubule binding observed on htau40 phosphorylation by the recombinant Ca2+/calmodulin (CaM)-dependent protein kinase II (CaM kinase II) alpha-subunit showed that CaM kinase II present in brain supernatant could participate in tau phosphorylation even in the absence of Ca2+/CaM and decrease tau-microtubule binding. In addition, use of htau40 mutants, htau40m1 (Ala416) and htau40m6 (Asp416), suggested that replacement of Ser416 by neutral or acidic amino acid produced some change in htau40 conformation that caused diminished binding with microtubules phosphorylated by brain supernatant in the presence of ethylene glycol bis(beta-aminoethyl ether) N, N'tetraacetic acid (EGTA). The change in conformation produced by Ser416 phosphorylation, however, was different from that produced by mutants since only nonmutated htau40 showed a significant decrease in binding with microtubules on phosphorylation by recombinant CaM kinase II in the presence of Ca2+/CaM compared to that obtained by phosphorylation in the presence of EGTA. This study showed that enhanced Ca2+/CaM-dependent protein kinase activity in DFP-treated hen brain supernatant may cause decreased tau-microtubule binding and destabilization of microtubules and may be involved in axonal degeneration in OPIDN.
二异丙基氟磷酸酯（DFP）可在母鸡、人类及其他敏感物种中引发有机磷酸酯诱导的迟发性神经毒性（OPIDN）。其特征为轻度共济失调，数日后会发展为严重共济失调或瘫痪。在超微结构上，OPIDN与中枢和外周神经系统轴突的退化有关。经DFP处理的母鸡脑上清液磷酸化的细菌表达的最长人类tau蛋白（htau40），与经对照母鸡脑上清液磷酸化的相比，在更短时间内微管结合能力下降。通过重组钙/钙调蛋白（CaM）依赖性蛋白激酶II（CaM激酶II）α亚基对htau40进行磷酸化时观察到的htau40 - 微管结合能力下降表明，脑上清液中存在的CaM激酶II即使在没有Ca2+/CaM的情况下也能参与tau磷酸化，并降低tau - 微管结合能力。此外，使用htau40突变体htau40m1（Ala416）和htau40m6（Asp416）表明，用中性或酸性氨基酸取代Ser416会使htau40构象发生一些变化，导致在存在乙二醇双（β - 氨基乙醚）N，N' - 四乙酸（EGTA）的情况下与脑上清液磷酸化的微管结合减少。然而，Ser416磷酸化产生的构象变化与突变体产生的不同，因为只有未突变的htau40在存在Ca2+/CaM的情况下经重组CaM激酶II磷酸化后与微管的结合能力与在存在EGTA的情况下磷酸化相比显著下降。这项研究表明，DFP处理的母鸡脑上清液中增强的Ca2+/CaM依赖性蛋白激酶活性可能导致tau - 微管结合减少和微管不稳定，并可能参与OPIDN中的轴突变性。
