Improvement of Protein Solubility in Macromolecular Crowding during Myoglobin Evolution
Improvement of Protein Solubility in Macromolecular Crowding during Myoglobin Evolution
复制标题
肌红蛋白进化过程中大分子拥挤中蛋白质溶解度的提高
DOI：
10.1021/acs.biochem.2c00166
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发表时间：
2022
期刊：
影响因子：
2.9
通讯作者：
Shirai Tsuyoshi
中科院分区：
文献类型：
--
作者：
Isogai Yasuhiro;Imamura Hiroshi;Sumi Tomonari;Shirai Tsuyoshi
活细胞的内部被极高浓度的生物分子所拥挤，因此在有机进化过程中，球状蛋白质应该已经被开发出来，以增加它们在这种拥挤条件下的溶解度。氧气储存蛋白肌红蛋白（Mb）是已知的，在潜水哺乳动物的肌细胞中的表达量远远大于陆地哺乳动物。我们以前已经复活了古代鲸鱼和鳍足类动物的肌球蛋白和实验证明，潜水动物肌球蛋白已经进化到在拥挤的条件下保持高溶解度或增加其对大分子沉淀剂的耐受性，而不是在稀释的缓冲溶液中的溶解度。然而，沉淀剂耐受性的化学机制的细节仍然不清楚。在这里，我们研究了pH依赖性的沉淀剂耐受性（β，相对于沉淀剂浓度的溶解度的斜率）现存的Mb和绘制的β值，以及祖先的Mb，对它们的表面净电荷（ZMb）。结果表明，沉淀剂耐受性可用ZM B的平方来近似，即β = aZMb 2 +B，其中a和b为常数。ZMb对沉淀的这种影响不能用经典的排除体积理论来预测，该理论给出Mb的常数β，但可以用Mb分子之间的静电排斥来解释。本研究阐明了Mb分子如何进化以增加其在体内的溶解度，并显示了天然Mb的中性或碱性等电点（pI）的生理意义，而不是酸性pI。
The inside of living cells is crowded by extremely high concentrations of biomolecules, and thus globular proteins should have been developed to increase their solubility under such crowding conditions during organic evolution. The O2-storage protein myoglobin (Mb) is known to be expressed in myocytes of diving mammals in much larger quantities than those of land mammals. We have previously resurrected ancient whale and pinniped Mbs and experimentally demonstrated that the diving animal Mbs have evolved to maintain high solubility under the crowding conditions or to increase their tolerance against macromolecular precipitants, rather than solubility in a dilute buffer solution. However, the detail of chemical mechanisms of the precipitant tolerance remains unclear. Here, we investigated pH dependence of the precipitant tolerance (β, slope of the solubility against precipitant concentration) of extant Mbs and plotted the β values, as well as those of ancestral Mbs, against their surface net charges (ZMb). The results demonstrated that the precipitant tolerance was approximated by the square ofZMb, that is, β =aZMb2+b, in whichaandbare constants. This effect ofZMbagainst the precipitation is not predicted by a classical excluded volume theory that gives constant β for Mbs but can be explained by electrostatic repulsion between Mb molecules. The present study elucidates how Mb molecules have evolved to increase theirin vivosolubility and shows the physiological significance of either neutral or basic isoelectric points (pI) of the natural Mbs, rather than acidic pI.