Mantulin W W, Rohde M F, Gotto A M, Pownall H J
J Biol Chem. 1980 Sep 10;255(17):8185-91.
The solution properties of human plasma apolipoprotein C-II (apoC-II) have been studied by analytical ultracentrifugation, circular dichroic spectroscopy, and fluorescence spectroscopy. ApoC-II self-associates in solution, even though no rigorous thermodynamic analysis of the mode of self-association could be established. The reversible denaturation of apoC-II by guanidinium chloride (GdmCl) proceeded in a sequential fashion. Initial disruption of protein self-association by 0.3 M GdmCl was followed by cooperative unfolding of monomeric protein at higher GdmCl concentratioans with a midpoint 1.1 M GdmCl. Based on tryptophan fluorescence quenching unfolded apoC-II was more permeable to penetration by small molecules than the self-associated protein. a very low free energy (delta GH2O = 2.8 kcal/mol) of denaturation was calculated from the GdmCl denaturation titration curve. Heating of apoC-II to 55 degrees C did not induce a reversible cooperative unfolding of the protein. Calculations, bsed on Chou-Fasman probability algorithms, reveal three sequential helical regions in apoC-II and one beta sheet structure (residues 61-74P. The locations of these regions are consistent with the known physiological functions of apoC-II.
通过分析超速离心、圆二色光谱和荧光光谱研究了人血浆载脂蛋白C-II（apoC-II）的溶液性质。尽管无法对自缔合模式进行严格的热力学分析，但apoC-II在溶液中会自缔合。氯化胍（GdmCl）对apoC-II的可逆变性是按顺序进行的。0.3 M GdmCl首先破坏蛋白质的自缔合，随后在较高GdmCl浓度下单体蛋白质协同展开，中点为1.1 M GdmCl。基于色氨酸荧光猝灭，未折叠的apoC-II比自缔合蛋白更容易被小分子穿透。根据GdmCl变性滴定曲线计算出极低的变性自由能（ΔGH2O = 2.8 kcal/mol）。将apoC-II加热至55℃不会诱导蛋白质发生可逆的协同展开。基于Chou-Fasman概率算法的计算揭示了apoC-II中有三个连续的螺旋区域和一个β折叠结构（第61 - 74位残基）。这些区域的位置与apoC-II已知的生理功能一致。
