Nejime T, Kinjoh K, Nakamura M, Hanashiro K, Sunagawa M, Eguchi Y, Kosugi T
1st Department of Physiology, School of Medicine, University of the Ryukyus, 207 Uehara, Nishihara, Okinawa, Japan.
Toxicon. 2000 Aug;38(8):1029-41. doi: 10.1016/s0041-0101(99)00215-9.
Habutobin, a thrombin-like enzyme from Trimeresurus flavoviridis venom, cleaves only the Arg(16)-Gly(17) bond in the rabbit Aalpha chain and releases fibrinopeptide A (FPA). To investigate the role of amino acid residues in the rabbit FPA sequence upon habutobin action, we examined the inhibitory effects of FPA and peptides containing partial sequences of FPA on the habutobin action. Fibrinopeptides from rabbit, human, bovine and dog were isolated and rabbit FPA was fragmented using dilute HCl. Rabbit FPA inhibited the action of habutobin although FPA from human, bovine and dog did not. Among the fragments of rabbit FPA, a heptapeptide Aalpha 3-9, the N-terminal region of rabbit FPA, competitively inhibited the release of FPA by habutobin, whereas the C-terminal hexapeptide of FPA (Aalpha 11-16) exerted no effect on the habutobin action. Synthetic tripeptides Ser-Thr-Phe corresponding to Aalpha 6-8 and Ala-Thr-Phe also inhibited the habutobin action, but Ser-Asp-Phe and Ala-Thr-Gly did not. It is concluded that habutobin would recognize the region around Thr(7)-Phe(8) in the sequence of rabbit FPA (Aalpha 1-16) prior to the cleavage of the Arg(16)-Gly(17) bond.
矛头蝮蛇毒素中的类凝血酶哈布托宾，仅能切割兔αA链中的精氨酸（16）-甘氨酸（17）键，并释放纤维蛋白肽A（FPA）。为了研究兔FPA序列中的氨基酸残基在哈布托宾作用中的作用，我们检测了FPA和含有FPA部分序列的肽对哈布托宾作用的抑制效果。分离了兔、人、牛和犬的纤维蛋白肽，并用稀盐酸将兔FPA片段化。兔FPA能抑制哈布托宾的作用，而人、牛和犬的FPA则不能。在兔FPA的片段中，七肽Aα3-9（兔FPA的N端区域）竞争性抑制哈布托宾释放FPA，而FPA的C端六肽（Aα11-16）对哈布托宾的作用没有影响。对应于Aα6-8的合成三肽丝氨酸-苏氨酸-苯丙氨酸和丙氨酸-苏氨酸-苯丙氨酸也能抑制哈布托宾的作用，但丝氨酸-天冬氨酸-苯丙氨酸和丙氨酸-苏氨酸-甘氨酸则不能。得出的结论是，在切割精氨酸（16）-甘氨酸（17）键之前，哈布托宾会识别兔FPA（Aα1-16）序列中苏氨酸（7）-苯丙氨酸（8）周围的区域。
