Naseem Farah, Khan Rizwan Hasan
Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh-202002, India.
Biochim Biophys Acta. 2005 May 25;1723(1-3):192-200. doi: 10.1016/j.bbagen.2005.02.009. Epub 2005 Mar 17.
When pea lectin was exposed to a low pH range, it was found that the secondary structure of the lectin resisted conformational changes to a large extent up to pH 2.4 and below this pH, a sharp transition was observed which could be due to the presence of 27 acidic amino acid residues present in the protein. The effects of 1,1,1,3,3,3 hexafluoro-isopropanol (HFIP) and 2,2,2-Trifluoroethanol (TFE) on the conformation of pea lectin at pH 2.4 were studied using circular dichroism and fluorescence spectroscopy. Analysis varying the TFE concentration showed that up to 80% TFE (v/v) protein retained the residual beta-structure accompanied by a loss in tertiary structure. A similar conformation is presumed to exist at 4% HFIP (v/v), with an increase in HFIP concentration structural rearrangements occurred and a transition from beta-structure to alpha-helical structure started from 12% HFIP which completed at 30% HFIP. Our studies show the occurrence of a common intermediate in the folding pathway of pea lectin induced by two different fluoroalcohols, which differ in their mode of action to stabilize the secondary structure of a given protein. While TFE was not found to induce any alpha-helical structure, HFIP caused the transition of pea lectin, which is predominantly a beta-sheet protein, to a structure rich in alpha-helical contacts. Thus, our results also point out the possibility of a non-hierarchical model of protein folding in lectins.
当豌豆凝集素暴露于低pH范围时，发现该凝集素的二级结构在pH值高达2.4时在很大程度上抵抗构象变化，而在该pH值以下，观察到急剧转变，这可能是由于该蛋白质中存在27个酸性氨基酸残基。使用圆二色性和荧光光谱研究了1,1,1,3,3,3-六氟异丙醇（HFIP）和2,2,2-三氟乙醇（TFE）对pH 2.4时豌豆凝集素构象的影响。分析不同TFE浓度时发现，高达80%（v/v）的TFE时蛋白质保留了残余的β-结构，同时三级结构丧失。推测在4%（v/v）的HFIP时存在类似的构象，随着HFIP浓度增加发生结构重排，从12%的HFIP开始从β-结构转变为α-螺旋结构，并在30%的HFIP时完成。我们的研究表明，在由两种不同氟代醇诱导的豌豆凝集素折叠途径中存在一个共同中间体，这两种氟代醇在稳定给定蛋白质二级结构的作用方式上有所不同。虽然未发现TFE诱导任何α-螺旋结构，但HFIP导致主要为β-折叠蛋白的豌豆凝集素转变为富含α-螺旋接触的结构。因此，我们的结果也指出了凝集素中蛋白质折叠的非层次模型的可能性。
