Oishi O, Yamashita S, Nishimoto E, Lee S, Sugihara G, Ohno M
Department of Chemistry, Faculty of Science, Kyushu University, Higashi-ku, Fukuoka, Japan.
Biochemistry. 1997 Apr 8;36(14):4352-9. doi: 10.1021/bi962171f.
Tachyplesin I, an antibacterial and antiviral heptadecapeptide from the hemocyte debris of Tachypleus tridentatus, contains four aromatic amino acids (Trp2, Phe4, Tyr8, and Tyr13) which have been shown to be crucial for activity. In order to investigate conformations and orientations of the aromatic amino acid residues of tachyplesin I in lipid bilayers, its analogs, [Phe8]- and/or [Phe13]-tachyplesin(s) I in which Tyr8 and Tyr13 are replaced by Phe, were synthesized. Circular dichroism spectral studies showed that three peptides are considerably different in conformation in aqueous solution at pH 8.0 whereas they take similar conformations in the presence of neutral egg yolk phosphatidylcholine (EYPC) liposomes. Energy transfer kinetics showed that the distances of Trp2-Tyr8 and Trp2-Tyr13 are 16 A (max of 18.3 A, min of 15.1 A) and 18 A (max of 20.2 A, min of 16.6 A) in buffer but are 12 A (max of 15.2 A, min of 8.6 A) and 18 A (max of 22.9 A, min of 12.9 A), respectively, in the presence of acidic EYPC/EYPG (3:1) liposomes. Decay kinetics for Trp2 fluorescence indicated that Trp2 takes at least three conformations in buffer and in acidic liposomes where fractions of three Trp2 conformers vary by changing the medium from buffer to acidic liposomes. Although tachyplesin I is not in amphiphilic structure in buffer in spite of its rigid antiparallel beta-conformation, its interaction with lipid bilayers appears to induce amphiphilic structure via minor alteration of peptide backbone and side chain orientations, resulting in shortening the distance of Trp2-Tyr8.
鲎素I是一种从中国鲎血细胞碎片中提取的具有抗菌和抗病毒活性的十七肽，含有四个芳香族氨基酸（Trp2、Phe4、Tyr8和Tyr13），这些氨基酸已被证明对活性至关重要。为了研究鲎素I中芳香族氨基酸残基在脂质双层中的构象和取向，合成了其类似物，即[Phe8]-和/或[Phe13]-鲎素I，其中Tyr8和Tyr13被Phe取代。圆二色光谱研究表明，这三种肽在pH 8.0的水溶液中构象有很大差异，而在中性蛋黄磷脂酰胆碱（EYPC）脂质体存在下它们具有相似构象。能量转移动力学表明，在缓冲液中Trp2-Tyr8和Trp2-Tyr13的距离分别为16 Å（最大值18.3 Å，最小值15.1 Å）和18 Å（最大值20.2 Å，最小值16.6 Å），而在酸性EYPC/EYPG（3:1）脂质体存在下，分别为12 Å（最大值15.2 Å，最小值8.6 Å）和18 Å（最大值22.9 Å，最小值12.9 Å）。Trp2荧光的衰减动力学表明，Trp2在缓冲液和酸性脂质体中至少有三种构象，三种Trp2构象的比例通过将介质从缓冲液变为酸性脂质体而发生变化。尽管鲎素I在缓冲液中尽管具有刚性的反平行β-构象但并非两亲结构，但其与脂质双层的相互作用似乎通过肽主链和侧链取向的微小改变诱导两亲结构，从而导致Trp2-Tyr8距离缩短
