Li A, Fenselau C, Kaltashov I A
Department of Chemistry and Biochemistry, University of Maryland Baltimore County, Baltimore, USA.
Proteins. 1998;Suppl 2:22-7.
The stability of single beta-strands and multistrand beta-pleated sheets as elements of secondary structure is examined in the absence of intermolecular interactions. Such experimental conditions (e.g., complete removal of solvent molecules and counterions) are achieved by placing the peptide ions in the gas phase. The metastable multiply- charged peptide ions produced by electrospray ionization undergo unimolecular dissociation. Intercharge repulsion within the precursor ions gives rise to the elevated kinetic energy of fragment ions, which is measured using Mass-analyzed Ion Kinetic Energy (MIKE) spectrometry. Intercharge distances calculated based on these measurements are compared to the numbers derived from molecular mechanics calculations with charge site assignments based on relative proton affinities. Evidence is presented suggesting that single beta-strands form collapsed structures in the absence of solvents, while multistrand beta-pleated sheets are likely to retain "native-like" secondary structures under the same conditions. These results indicate that intramolecular hydrogen bonds are the major factor determining the three-dimensional arrangements of polypeptides in the gas phase, compensating both long- and short-range electrostatic repulsions. This is in good agreement with our earlier findings (Proteins 27:165170, 1997) concerning stability of helical conformation of melittin in the absence of solvent.
在不存在分子间相互作用的情况下，研究了单β链和多链β折叠片作为二级结构元件的稳定性。通过将肽离子置于气相中来实现这样的实验条件（例如，完全去除溶剂分子和抗衡离子）。电喷雾电离产生的亚稳多电荷肽离子发生单分子解离。前体离子内的电荷间排斥导致碎片离子的动能升高，这通过质量分析离子动能（MIKE）光谱法进行测量。基于这些测量计算出的电荷间距离与基于相对质子亲和力进行电荷位点分配的分子力学计算得出的数值进行比较。有证据表明，在没有溶剂的情况下，单β链形成塌陷结构，而多链β折叠片在相同条件下可能保留“类似天然”的二级结构。这些结果表明，分子内氢键是决定气相中多肽三维排列的主要因素，它补偿了长程和短程静电排斥。这与我们早期关于在没有溶剂的情况下蜂毒肽螺旋构象稳定性的研究结果（《蛋白质》27:165 - 170, 1997）非常一致。
