J Biol Chem, Vol. 274, Issue 37, 26172-26178, September 10, 1999

Horseshoe Crab Hemocyte-derived Antimicrobial Polypeptides, Tachystatins, with Sequence Similarity to Spider Neurotoxins

Tsukasa Osaki, Miyuki Omotezako^§, Ranko Nagayama^§, Michimasa Hirata^¶, Sadaaki Iwanaga^§, Jiro Kasahara, Junji Hattori^§, Isao Ito^§, Hiroyuki Sugiyama^§, and Shun-ichiro Kawabata^§

From the  Department of Molecular Biology, Graduate School of Medical Science, Fukuoka 812-8582, the ^§ Department of Biology, Kyushu University, Fukuoka 812-8581, and the ^¶ Department of Bacteriology, Iwate Medical University, Morioka 020-8505, Japan

Antimicrobial peptides, named tachystatins A, B, and C, were identified from hemocytes of the horseshoe crab Tachypleus tridentatus. Tachystatins exhibited a broad spectrum of antimicrobial activity against Gram-negative and Gram-positive bacteria and fungi. Of these tachystatins, tachystatin C was most effective. Tachystatin A is homologous to tachystatin B, but tachystatin C has no significant sequence similarity to tachystatins A and B. Tachystatins A and B showed sequence similarity to -agatoxin-IVA of funnel web spider venom, a potent blocker of voltage-dependent calcium channels. However, they exhibited no blocking activity of the P-type calcium channel in rat Purkinje cells. Tachystatin C also showed sequence similarity to several insecticidal neurotoxins of spider venoms. Tachystatins A, B, and C bound significantly to chitin. A causal relationship was observed between chitin binding activity and antifungal activity. Tachystatins caused morphological changes against a budding yeast, and tachystatin C had a strong cell lysis activity. The septum between mother cell and bud, a chitin-rich region, was stained by fluorescence-labeled tachystatin C, suggesting that the primary recognizing substance on the cell wall is chitin. As horseshoe crab is a close relative of the spider, tachystatins and spider neurotoxins may have evolved from a common ancestral peptide, with adaptive functions.