Lee In Su, Long Jeffrey R, Prusiner Stanley B, Safar Jiri G
Department of Chemistry, University of California, Berkeley, California 94720-1460, USA.
J Am Chem Soc. 2005 Oct 12;127(40):13802-3. doi: 10.1021/ja055219y.
The efficacy of a variety of polyoxometalate anions in selectively precipitating the infectious isoform of the prion protein (PrPSc) over the normal, cellular protein (PrPC) was tested as a means of improving the sensitivity of a conformation-dependent immunoassay (CDI). Experiments utilizing neutralized aqueous solutions containing MgCl2.6H2O and Na2H[PW12O40] (1) indicated that use of the former is detrimental to selectivity, while use of the latter gives optimal selectivity at a concentration of 2.48% w/v, much higher than the 0.31% w/v employed in the current CDI protocol. Similar experiments using Na4[SiW12O40] (2), K5[BW12O40] (3), and Na6[H2W12O40] (4) were performed to probe the role of charge density in polyoxometalate anions possessing the Keggin structure. These, coupled with assignment of solution structures via NMR and infrared spectroscopy, revealed the following trend in optimal concentrations: [HBW11O39]8- < [SiW11O39]8- < [PW11O39]7- = [H2W12O40]6-. Interestingly, use of the salts K10[Zn4(H2O)2(PW9O34)2] (5), Na16[Zn4(H2O)2(P2W15O56)2] (6), and Na27[NaAs4W40O140] (7), containing larger polyoxometalate anions, was found to suppress PrPSc precipitation in a concentration-dependent manner. Taken together, the results suggest a precipitation mechanism wherein Keggin-type anions link multiple PrPSc moieties by binding a somewhat hindered cleft featuring one or more positively charged residues.
测试了多种多金属氧酸盐阴离子在选择性沉淀朊病毒蛋白（PrPSc）的感染性异构体而非正常细胞蛋白（PrPC）方面的功效，以此作为提高构象依赖性免疫测定（CDI）灵敏度的一种手段。利用含有MgCl₂·6H₂O和Na₂H[PW₁₂O₄₀]（1）的中和水溶液进行的实验表明，使用前者对选择性不利，而使用后者在浓度为2.48% w/v时具有最佳选择性，这一浓度远高于当前CDI方案中使用的0.31% w/v。使用Na₄[SiW₁₂O₄₀]（2）、K₅[BW₁₂O₄₀]（3）和Na₆[H₂W₁₂O₄₀]（4）进行了类似实验，以探究电荷密度在具有Keggin结构的多金属氧酸盐阴离子中的作用。这些实验，再结合通过核磁共振和红外光谱对溶液结构的归属，揭示了最佳浓度的以下趋势：[HBW₁₁O₃₉]⁸⁻ < [SiW₁₁O₃₉]⁸⁻ < [PW₁₁O₃₉]⁷⁻ = [H₂W₁₂O₄₀]⁶⁻。有趣的是，发现使用含有较大多金属氧酸盐阴离子的盐K₁₀[Zn₄(H₂O)₂(PW₉O₃₄)₂]（5）、Na₁₆[Zn₄(H₂O)₂(P₂W₁₅O₅₆)₂]（6）和Na₂₇[NaAs₄W₄₀O₁₄₀]（7）会以浓度依赖性方式抑制PrPSc沉淀。综合来看，结果表明了一种沉淀机制，其中Keggin型阴离子通过结合一个具有一个或多个带正电荷残基的有点受阻的裂缝来连接多个PrPSc部分。
