PolyA,PolyU及双链复合物PolyA·PolyU的拉曼光谱研究

测试了PolyA,PolyU及其双链复合物Po1yA·PolyU的拉曼光谱,研究了双链形成前后的光谱变化.结果显示:(1)15℃下,在pH 7.0的0.14 mol.L-1 NaCl,1 mmol·L-1 Tris水溶液中,PolyU, PolyA,PolyA·PolyU分别以无规卷曲、A型单螺旋和A型双螺旋结构存在.后两种结构区别于前者的主 要光谱标志之一是有序结构在814 cm-1附近出现的拉曼峰.另一光谱标志则是1 100cm-1附近的谱峰半高宽的大小.PolyA,PolyA·PolyU在该处有着相同的半高宽,而PolyU在该处的谱峰则有明显的展宽.此外,还发现PolyA的有序程度不及PolyA·PolyU,这可以从(813±2)cm-1与1 100 cm-1的峰强比推知;(2)PolyU,PolyA形成双螺旋复合物之后,多聚核苷酸碱基-碱基堆积力大为增强,主链构象变得更为有序化,从而产生了明显的拉曼减色效应并伴随着相关谱带的频移.在这个过程中,PolyU链比PolyA链所产生的光谱变化更为显著.该研究表明,从这类实验结果中提取特征光谱标志有望实现基因芯片的拉曼光谱检测.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Involvement of non-polyalanine (polyA) residues in aggregation of polyA proteins: Clue for inhibition of aggregation

Presence of polyalanine (polyA) stretches in some proteins is found to be associated with their aggregation, which causes disorders in various developmental processes. In this work, inherent propensities towards aggregation of some residues, which are not part of the polyA stretches, have been identified by using the primary sequences of seven polyA proteins with the help of Betascan, PASTA and Tango programs and explored unambiguously. This provides a basis for proposing molecular mechanism of this type of aggregation. Reported suppression of aggregation of polyA proteins by chaperones like HSP40 and HSP70 is substantiated through molecular docking. The hydrophobic residues of identified aggregating region are found to be interacting with hydrophobic surface of chaperones. This suggests a crucial clue for possible way to inhibit the aggregation of such proteins.     

Raman spectroscopic study of G--A mismatches

G-A mismatches are non-canonical base pairs that widely occur in native nucleic acids. They have been found to be functionally important in adopting unusual structures. In this paper, G-A mispairing was studied by Raman spectral characterization of Polyadenylic acid （PolyA）, Polyguanylic acid （PolyG） and their equimolar mixture in solution of 0.08 mol/L Na^＋, pH7.0. The experiment showed the following three results. （1） At the experimental conditions used in the present work, PolyA and G A complexes existed as single-stranded and double-stranded helix of A form, respectively. And PolyG mainly occurred to be anti-parallel quadruplex conformers. （2） The formation of G A complexes, on one hand strengthened parts of base stacking interactions especially for PolyG, leading to Raman hypochromism effect with some corresponding bands shifting, and on the other hand weakened other base stacking interactions especially for PolyA to a certain degree. During this process, the backbone of PolyG underwent a significant change, but PolyA still conserved its main chain conformation. （3） The formation of G A complexes was stabilized by two interbase hydrogen- bond interactions （i.e. N6H2（A）-N3 （G） and N7 （A）--N2H2（G）） and a third hydrogen bond between O2^＋ （G） and N6 （A）. The third hydrogen bond was responsible for the remarkable changes of PolyG backbone conformation.[第一段]