Nose T, Fujita T, Nakajima M, Inoue Y, Costa T, Shimohigashi Y
Laboratory of Biochemistry, Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka, 812-8581, Japan.
J Biochem. 1998 Aug;124(2):354-8. doi: 10.1093/oxfordjournals.jbchem.a022119.
Phenylalanine at position 2 of thrombin receptor-tethered ligand peptide (SFLLRNP) is crucially important for the activation of thrombin receptor. Its substitution by para-fluorophenylalanine [(p-F)Phe] enhanced several times the activity in human epithelial-like SH-EP cells [Nose et al. (1993) Biochem. Biophys. Res. Commun. 193, 694-699]. To clarify the interaction mode of Phe-2-phenyl in receptor activation, a series of analogs having chemical modifications on the benzene ring of Phe-2 were synthesized and examined for their ability to induce the aggregation of human platelets. When the fluorine atom was placed at the meta or ortho position, the resulting analogs exhibited considerably diminished activity (about 10-20% of para-derivative), indicating that the substitution is allowed only at the para position. The derivative with pentafluorophenylalanine was totally devoid of activity. These results suggested that Phe-2 requires hydrogen atom(s) on the benzene ring presumably for interaction with the receptor. No activity enhancement was observed for analogs with para-chloro-, bromo-, or iodophenylalanine, indicating the importance of the high electronegativity of fluorine to intensify the dipole of CH(s) remaining in the Phe-2-benzene ring. Inactivity of analogs having para-iodophenylalanine and homophenylalanine indicated the importance of the size of para substituents, and the placement of hydroxyl, nitro, and trifluoromethyl groups at the para position led to no activity. The interaction of Phe-2 of SFLLRNP appeared to be structurally restricted to a limited space in the receptor. The results suggested the presence of face-to-edge pi-pi interaction based upon the CH/pi interaction between the ligand Phe-2-phenyl group and the receptor aromatic group.
凝血酶受体连接配体肽（SFLLRNP）第2位的苯丙氨酸对于凝血酶受体的激活至关重要。用对氟苯丙氨酸[（p-F）Phe]取代它可使在人上皮样SH-EP细胞中的活性增强数倍[Nose等人（1993年），《生物化学与生物物理研究通讯》，193，694 - 699]。为阐明第2位苯丙氨酸的苯基在受体激活中的相互作用模式，合成了一系列对第2位苯丙氨酸苯环进行化学修饰的类似物，并检测它们诱导人血小板聚集的能力。当氟原子位于间位或邻位时，所得类似物的活性显著降低（约为对位衍生物的10 - 20%），表明这种取代仅允许在对位进行。五氟苯丙氨酸衍生物完全没有活性。这些结果表明，第2位苯丙氨酸的苯环上可能需要氢原子与受体相互作用。对氯、溴或碘苯丙氨酸类似物未观察到活性增强，表明氟的高电负性对于增强第2位苯丙氨酸苯环中剩余的CH(s)偶极的重要性。对碘苯丙氨酸和高苯丙氨酸类似物无活性表明对位取代基大小的重要性，并且在对位放置羟基、硝基和三氟甲基基团导致无活性。SFLLRNP第2位苯丙氨酸的相互作用在结构上似乎局限于受体中的有限空间。结果表明基于配体第2位苯丙氨酸苯基与受体芳香基团之间的CH/π相互作用存在面对面边缘π-π相互作用。
