Damaschun G, Damaschun H, Gast K, Zirwer D
Institut für Biologie der Humboldt-Universität zu Berlin, Germany.
Biochemistry (Mosc). 1998 Mar;63(3):259-75.
Structures of proteins in unfolded states have important implications for the protein folding problem and for the translocation of polypeptide chains. Acid-denatured, cold-denatured, and 6 M guanidine hydrochloride (GuHCl) denatured yeast phosphoglycerate kinase (PGK) are ensembles of flexible unfolded molecules with rapidly interconverting structures of the individual polypeptide chains. They differ, however, in their physical properties, such as in coil size and in stiffness over a short distance along the chain. These properties of polypeptide chains can be described well by persistence statistics. A solution containing 0.7 M GuHCl at 4.5 degrees C is nearly a Theta-solvent for PGK. By contrast, 6 M GuHCl is a good solvent for PGK. Acid-denatured PGK at low ionic strength has the most expanded and stiffest chains. The conformation of heat-denatured PGK should be more compact than that of random walk chains at the Theta-point, as can be inferred from measurements on other proteins. Investigations of heat-denatured PGK by scattering methods are unfeasible due to aggregation of the protein. The persistence length as a measure of chain stiffness varies between a = 1.74 nm for cold-denatured PGK and a = 3.0 nm for acid-denatured PGK. The distribution functions of the gyration radii were calculated from the X-ray scattering data for all unfolded states and compared with the radius of gyration of the natively folded molecule.
未折叠状态下蛋白质的结构对于蛋白质折叠问题以及多肽链的转运具有重要意义。酸变性、冷变性以及6 M盐酸胍（GuHCl）变性的酵母磷酸甘油酸激酶（PGK）是具有柔性未折叠分子的集合体，其中单个多肽链的结构会快速相互转换。然而，它们在物理性质上存在差异，例如在卷曲大小以及沿链短距离的刚性方面。多肽链的这些性质可以通过持久统计很好地描述。在4.5摄氏度下含有0.7 M GuHCl的溶液对于PGK而言近乎是一个θ溶剂。相比之下，6 M GuHCl是PGK的良溶剂。低离子强度下酸变性的PGK具有最伸展且最刚性的链。热变性PGK的构象应该比在θ点的无规行走链的构象更紧凑，这可以从对其他蛋白质的测量中推断出来。由于蛋白质的聚集，通过散射方法研究热变性的PGK是不可行的。作为链刚性度量的持久长度在冷变性PGK的a = 1.74 nm和酸变性PGK的a = 3.0 nm之间变化。从所有未折叠状态的X射线散射数据计算出回转半径的分布函数，并与天然折叠分子的回转半径进行比较。
