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Protein crystals as a key for deciphering macromolecular crowding effects on biological reactions

机译:蛋白质晶体作为解体大分子挤压对生物反应的影响的关键

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摘要

When placed in the same environment, biochemically unrelated macromolecules influence each other's biological function through macromolecular crowding (MC) effects. This has been illustratedin vitroby the effects of inert polymers on protein stability, protein structure, enzyme kinetics and protein aggregation kinetics. While a unified way to quantitatively characterize MC is still lacking, we show that the crystal solubility of lysozyme can be used to predict the influence of crowding agents on the catalytic efficiency of this enzyme. In order to capture general enthalpic effects, as well as hard entropic effects that are specific of large molecules, we tested sucrose and its cross-linked polymer Ficoll-70 as additives. Despite the different conditions of pH and ionic strength adopted, both the crystallization and the enzymatic assays point to an entropic contribution of approximately -1 kcal mol(-1)caused by MC. Our results demonstrate that the thermodynamic activity of proteins is markedly increased by the reduction of accessible volume caused by the presence of macromolecular cosolutes. Unlike what is observed in protein folding studies, this MC effect cannot be reproduced using equivalent concentrations of monomeric crowding units. Applicable to any crystallizable protein, the thermodynamic interpretation of MC based on crystal solubility is expected to help in elucidating the full extent and importance of hard-type interactions in the crowded environment of the cell.
机译:当放置在相同的环境中,生物化学上无关的大分子通过大分子拥挤(MC)效应来影响彼此的生物学功能。这已被鉴于植物素的惰性聚合物对蛋白质稳定性,蛋白质结构,酶动力学和蛋白质聚集动力学的影响。虽然仍然缺乏定量表征MC的统一方式,但我们表明溶菌酶的晶体溶解度可用于预测拥挤试剂对该酶催化效率的影响。为了捕获一般焓效应,以及具有大分子特异性的硬熵效应,我们测试蔗糖及其交联聚合物Ficoll-70作为添加剂。尽管采用了不同的pH和离子强度的条件,但结晶和酶测定均指向由MC引起的约-1kcal摩尔(-1)的熵贡献。我们的研究结果表明,通过通过存在大分子溶解的存在引起的可接近体积的减少显着增加了蛋白质的热力学活性。与蛋白质折叠研究中观察到的不同,不能使用等同的单体挤压单元再现该MC效应。适用于任何可结晶蛋白质,基于晶体溶解性的MC热力学解释有助于阐明细胞拥挤环境中硬型相互作用的全部程度和重要性。

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