Pispisa B, Stella L, Venanzi M, Palleschi A, Polese A, Formaggio F, Toniolo C
Dipartimento di Scienze e Tecnologie Chimiche, Universitá di Roma Tor Vergata, Italy.
J Pept Res. 2000 Nov;56(5):298-306. doi: 10.1034/j.1399-3011.2000.00772.x.
In continuation of our studies on the determination of the structural features of functionalized peptides in solution by combining time-resolved fluorescence data and molecular mechanics results, the conformational properties of a series of linear, homo-Aib peptides in methanol (a structure-supporting solvent) were investigated. These compounds have the general formula P(Aib)nN, where Aib is alpha-aminoisobutyric acid, N is naphthalene and P is the monomethylated protoporphyrin IX, the two latter chromophores being covalently attached to the peptide C- and N-termini, respectively, while n=3, 6 and 9. According to 1H NMR and IR spectra, the peptides investigated largely populate a 3(10)-helical structure in CDCl3, which is also a structure-supporting solvent. Both steady-state and time-resolved fluorescence measurements show a strong quenching of the N emission that parallels an increase of the P fluorescence intensity, suggesting the occurrence of long-range energy transfer from 1N* to ground-state P. Comparison of quenching efficiencies and lifetime pre-exponents with those obtained theoretically from the deepest energy minimum conformers is very satisfactory. The computed structures, built up by partially taking into account the solvent medium, exhibit a rigid, highly compact arrangement, owing to both the 3(10)-helix conformation of the backbone chain and the very few peptide-to-chromophore covalent linkages. As a result, only one or two stable conformations for each peptide were theoretically found, in full agreement with the time-resolved fluorescence data. Orientational effects between the probes must be taken into account for a correct interpretation of the fluorescence decay results, which implies that interconversion among conformational substates of the N linkages is slower than 10 ns, corresponding to the upper limit of the energy transfer characteristic time.
为了继续我们通过结合时间分辨荧光数据和分子力学结果来确定溶液中功能化肽结构特征的研究，我们研究了一系列线性同型Aib肽在甲醇（一种结构支持溶剂）中的构象性质。这些化合物的通式为P(Aib)nN，其中Aib是α-氨基异丁酸，N是萘，P是单甲基化原卟啉IX，后两个发色团分别共价连接到肽的C端和N端，而n = 3、6和9。根据1H NMR和IR光谱，所研究的肽在CDCl3（也是一种结构支持溶剂）中主要呈现3(10)-螺旋结构。稳态和时间分辨荧光测量均显示N发射的强烈猝灭，这与P荧光强度的增加平行，表明发生了从1N*到基态P的长程能量转移。将猝灭效率和寿命预指数与从最深能量最低构象理论上获得的结果进行比较，结果非常令人满意。通过部分考虑溶剂介质构建的计算结构，由于主链的3(10)-螺旋构象和肽与发色团之间极少的共价连接，呈现出刚性、高度紧凑的排列。因此，理论上每个肽仅发现一两种稳定构象，这与时间分辨荧光数据完全一致。为了正确解释荧光衰减结果，必须考虑探针之间的取向效应，这意味着N连接的构象亚态之间的相互转换慢于10 ns，这对应于能量转移特征时间的上限。
