The exclusion of glycine betaine from anionic biopolymer surface: Why glycine betaine is an effective osmoprotectant but also a compatible solute
The exclusion of glycine betaine from anionic biopolymer surface: Why glycine betaine is an effective osmoprotectant but also a compatible solute
复制标题
DOI：
10.1021/bi049115w
复制
发表时间：
2004-11-23
期刊：
影响因子：
2.9
通讯作者：
Record, MT
中科院分区：
文献类型：
--
作者：
Felitsky, DJ;Cannon, JG;Record, MT
特别地，甘氨酸甜菜碱（N，N，N-三甲基甘氨酸; GB）在体内既是有效的细胞保护剂（有效增加细胞质渗透压和生长速率）又是相容的溶质（对生物聚合物功能没有有害影响，包括稳定性和活性）。对于GB是一种有效的生物保护剂，但不会大大影响生物聚合物的稳定性，我们预测，它必须与折叠的蛋白质表面的相互作用非常不同，而不是暴露在展开。为了验证这个假设，我们用圆二色谱定量了GB与在展开边缘稳定的lacI螺旋-转角-螺旋（HTH）DNA结合域时暴露的相对不带电表面的优先相互作用，用全重量蒸气压渗透法（VPO）定量了GB与折叠的鸡蛋白色溶菌酶（HEWL）和牛血清白蛋白（BSA）的更高电荷表面的优先相互作用，并将这些结果与VPO研究的结果进行了比较（Hong等，（2004），Biochemistry，43，14744-14758）。对于这四种生物聚合物表面，我们观察到，每单位生物聚合物表面积的GB排除的程度随着阴离子氧（蛋白质羧酸盐或DNA磷酸盐）表面的分数的增加而强烈增加。此外，GB从解折叠lacI HTH时暴露的表面和从HEWL的折叠表面排除的程度比从其阴离子表面的小部分预期的要高，这与GB从极性酰胺表面的适度排除一致，如通过蛋白质稳定性的疏水模型预测的（Bolen和Baskakov（2001）J. Mol. Biol. 310，955-963）。GB从阴离子表面的强排斥解释了它如何既可以是有效的疏水保护剂又可以是相容的溶质;对这种排斥的分析产生了两层水的阴离子蛋白质羧酸盐表面的水合作用的下限（大于或等于0.22 H2O埃（-2））。
Paradoxically, glycine betaine (N,N,N-trimethyl glycine; GB) in vivo is both an effective osmoprotectant (efficient at increasing cytoplasmic osmolality and growth rate) and a compatible solute (without deleterious effects on biopolymer function, including stability and activity). For GB to be an effective osmoprotectant but not greatly affect biopolymer stability, we predict that it must interact very differently with folded protein surface than with that exposed in unfolding. To test this hypothesis, we quantify the preferential interaction of GB with the relatively uncharged surface exposed in unfolding the marginally stable lacI helix-turn-helix (HTH) DNA binding domain using circular dichroism and with the more highly charged surfaces of folded hen egg white lysozyme (HEWL) and bovine serum albumin (BSA) using all-gravimetric vapor pressure osmometry (VPO) and compare these results with results of VPO studies (Hong et al. (2004), Biochemistry, 43, 14744-14758) of the interaction of GB with polyanionic duplex DNA. For these four biopolymer surfaces, we observe that the extent of exclusion of GB per unit of biopolymer surface area increases strongly with increasing fraction of anionic oxygen (protein carboxylate or DNA phosphate) surface. In addition, GB is somewhat more excluded from the surface exposed in unfolding the lacI HTH and from the folded surface of HEWL than expected from their small fraction of anionic surface, consistent with moderate exclusion of GB from polar amide surface, as predicted by the osmophobic model of protein stability (Bolen and Baskakov (2001) J. Mol. Biol. 310, 955-963). Strong exclusion of GB from anionic surface explains how it can be both an effective osmoprotectant and a compatible solute; analysis of this exclusion yields a lower bound on the hydration of anionic protein carboxylate surface of two layers of water (greater than or equal to0.22 H2O Angstrom(-2)).