Zhuang P, Li H, Williams J G, Wagner N V, Seiffert D, Peterson C B
Department of Biochemistry, University of Tennessee, Knoxville, Tennessee 37996, USA.
J Biol Chem. 1996 Jun 14;271(24):14333-43. doi: 10.1074/jbc.271.24.14333.
Unfolding and refolding of plasma vitronectin appear irreversible under near physiological conditions, with rearrangements of disulfides and self-association to a multimeric form observed as prominent structural alterations which accompany denaturation. A mechanism for the folding reactions of vitronectin has been proposed (Zhuang, P., Blackburn, M. N., and Peterson, C. B.(1996) J. Biol. Chem. 270, 14323-14332) in which vitronectin acquires a partially folded intermediate structure which is highly prone to oligomerize into a multimeric form. Strongly oxidizing conditions adopted for refolding from urea were effective at preventing disulfide rearrangement which disrupts distal disulfides near the C terminus of the protein. Prohibiting disulfide rearrangement under these conditions, however, was not sufficient to achieve reversibility in folding. In contrast, variations in the ionic strength of the refolding medium affect the partitioning of species so that refolded monomers are obtained at high ionic strength, and self-association is precluded. The effects of ionic strength on the partially folded intermediate in the vitronectin folding pathway appear to favor intramolecular hydrophobic collapse to form a stable hydrophobic core for the monomer versus intermolecular hydrophobic interactions which stabilize multimeric vitronectin. Although both ionic and hydrophobic interactions presumably contribute to subunit interfaces within the multimer, the basic heparin-binding region near the C terminus of the protein does not provide binding interactions which are important for self-association of vitronectin.
在接近生理条件下，血浆玻连蛋白的去折叠和再折叠似乎是不可逆的，二硫键重排和自缔合形成多聚体形式是观察到的伴随变性的显著结构改变。已经提出了一种玻连蛋白折叠反应的机制（庄，P.，布莱克本，M. N.，和彼得森，C. B.（1996年）《生物化学杂志》270，14323 - 14332），其中玻连蛋白获得一种部分折叠的中间结构，这种结构极易寡聚成多聚体形式。从尿素中重折叠所采用的强氧化条件有效地防止了二硫键重排，而二硫键重排会破坏蛋白质C末端附近的远端二硫键。然而，在这些条件下禁止二硫键重排不足以实现折叠的可逆性。相比之下，重折叠介质离子强度的变化会影响物种的分配，从而在高离子强度下获得重折叠的单体，并防止自缔合。离子强度对玻连蛋白折叠途径中部分折叠中间体的影响似乎有利于分子内疏水塌缩以形成单体的稳定疏水核心，而不利于稳定多聚体玻连蛋白的分子间疏水相互作用。尽管离子相互作用和疏水相互作用可能都对多聚体内的亚基界面有贡献，但蛋白质C末端附近的碱性肝素结合区域并未提供对玻连蛋白自缔合很重要的结合相互作用。
