New Structural Motifs Found in Inverterate Proteins.

由于无脊椎动物的多样性，人们有望在无脊椎动物蛋白质中发现许多新的结构和功能。特别是，无脊椎动物的防御系统，即所谓的先天免疫，包括血淋巴凝固和酚氧化酶介导的黑化，是由外来物质诱导的，导致入侵微生物的吞噬。这些固定的入侵者最终会被主要从各种血细胞释放的抗菌物质杀死。尽管没有免疫球蛋白本身，无脊椎动物血淋巴能够对入侵者做出高度特异性的反应。作者重点研究了无脊椎动物、河蟹和线虫体内的新防御分子。速殖素是从河蟹血细胞中分离出来的一种抗菌蛋白。求解的结构由五个二硫键稳定，涉及一个三股反平行的β-Sheet。结果表明，N-末端和C-末端是柔性的，没有规则的二级结构。Tachycitin与已知的几丁质结合蛋白的结构比较表明，Tachycitin的局部结构(40-60个残基)与植物几丁质结合蛋白相似。Tchystatin也是从河蟹血细胞中分离出来的一种抗菌蛋白。根据NOESY谱分析和结构计算，Tachystatin A的二级结构的主要元素是其主要结构基序为+2x，-1的三链β-Sheet。Tachystatin A的三维结构与漏斗网蜘蛛毒液中发现的钙通道阻滞剂ω-Aagatoxin IVA相似。ASABF(A.suum抗菌因子)是在猪蛔虫体液中发现的一种抗菌蛋白。ASABF的二级结构由一个α-螺旋和一个β-折叠组成，与昆虫防御素的基序相同。

Many new structures and functions are expected to be found in invertebrate proteins because of the diversity of invertebrate animals. In particular, invertebrate defense systems, so-called innate immunity, include hemolymph coagulation and phenoloxidase-mediated melanization are induced by foreign substances, that result in the engulfment of invading microorganisms. These immobilized invaders are finally killed by antimicrobial substances released mainly from various hemocytes. In spite of the absence of immunoglobulin itself, the invertebrate hemolymph is capable of responding with a high degree of specificity against invaders. The authors focused on the new defense molecules in the invertebrate animals, horseshoe crab and nematode.Tachycitin is an antimicrobial protein isolated from hemocytes of horseshoe crab, Tachypleus tridentatus. The solved structure is stabilized by five disulfide bridges, involving a three stranded antiparallel β-sheet. It is found that the N- and C-terminal are flexible and without regular secondary structures. Structural comparison between tachycitin and the known chitin-binding proteins reveals that the local structure (residues 40-60) of tachycitin is similar to that of plant chitin-binding proteins.Tchystatin is also an antimicrobial protein isolated from hemocytes of horseshoe crab, Tachypleus tridentatus. From NOESY spectra analyses and structure calculations, the main element of secondary structure of tachystatin A is its triple- stranded β-sheet of classificaton +2x, -1 as its dominant structural motif. The three-dimensional structure of tachystatin A is similar with that of calcium channel blocker ω-agatoxin IVA found in venom of funnel web spider.ASABF (A. suum antibacterial factor) is an antimicrobial protein found in the body fluid of the nematode Ascaris suum. The secondary structure of ASABF is composed of one α-helix and one β-sheet like as the motif of insect defensin.