Endo T, Kim H S, Maeda N, Tamiya N, Miyazawa T
J Biochem. 1986 Mar;99(3):681-91. doi: 10.1093/oxfordjournals.jbchem.a135527.
The 270-MHz proton NMR spectra of the unique long neurotoxins bearing Phe-25, Astrotia stokesii b (As b) and Astrotia stokesii c (As c) from Astrotia stokesii, and Acanthophis antarcticus b (Aa b) from Acanthophis antarcticus, have been analyzed. The aromatic proton resonances of Phe-25 in As b and Aa b were assigned on the basis of the nuclear Overhauser effects observed on irradiation of slowly exchanging amide protons. Phe-25 was found to be involved in hydrophobic interactions with Ile/Val-42, Ala-46 and Ile-58 in As b and As c, and with Ala-46 and Val-58 in Aa b. These hydrophobic interactions, instead of the hydrogen bond between Tyr-25 and Glu-42 found in other neurotoxins, appear to be important for maintenance of the biologically active tertiary structure. The pH dependency of the chemical shift and intensity of the Trp-72 N-1 proton resonance of As b indicates that the indole ring is not fully exposed to the solvent and that the extra tail segment of this long neurotoxin interacts with the main part of the molecule.
对来自斯托克斯星蝰（Astrotia stokesii）的带有苯丙氨酸-25（Phe-25）的独特长神经毒素斯托克斯星蝰b（As b）和斯托克斯星蝰c（As c），以及来自南极棘蛇（Acanthophis antarcticus）的南极棘蛇b（Aa b）的270兆赫质子核磁共振谱进行了分析。基于对缓慢交换酰胺质子辐照时观察到的核Overhauser效应，确定了As b和Aa b中Phe-25的芳香族质子共振峰。研究发现，在As b和As c中，Phe-25与异亮氨酸/缬氨酸-42、丙氨酸-46和异亮氨酸-58存在疏水相互作用，而在Aa b中，Phe-25与丙氨酸-46和缬氨酸-58存在疏水相互作用。这些疏水相互作用，而非其他神经毒素中发现的酪氨酸-25（Tyr-25）和谷氨酸-42（Glu-42）之间的氢键，似乎对维持生物活性三级结构很重要。As b的色氨酸-72（Trp-72）N-1质子共振峰的化学位移和强度对pH的依赖性表明，吲哚环并未完全暴露于溶剂中，且这种长神经毒素的额外尾部片段与分子的主要部分相互作用。
