兩棲類的皮膚分泌物富含抗菌蛋白，為遭遇微生物的侵襲時的第一道防線。本論文研究的抗菌蛋白，Maximin H5，是來自於Bombina maxima（大蹼蟾蜍）的皮膚分泌物。從過去的文獻得知，Maximin H5是由大蹼蟾蜍的皮膚的先驅蛋白質，經由後轉譯修飾作用所切割出的一段新胜肽。分析其氨基酸組成，發現它包含三個酸性Asp氨基酸但不含任何鹼性氨基酸，而且似乎僅對革蘭氏陽性菌有抗菌的效果。
至今，酸性抗菌胜肽被發現的很少，對於它的蛋白質三度結構與抗菌機制的相關性了解得不多。本論文，即針對酸性胜肽之一的Maximin H5進行三度空間結構之探討，我們利用核磁共振光譜和結構計算法，來決定Maximin H5之三度空間結構，並針對其結構特性推衍其作用機制。
從化學位移指標預測其二級結構的結果來看，其結構在C-端有helix的結構，但運算所得的三度空間結構並無明顯的helix存在；另外從表面電荷分析圖顯示，Maximin H5不像一般的鹼性抗菌胜肽具兩性結構；加上它帶負電荷的特性，不易親近細菌外膜。綜合以上之結果，推測其抗菌功能不是直接作用在細菌外膜上。

Amphibian skin is a rich resource of antimicrobial peptides, serves as the first line of defense of creatures attacked by microbes. The antimicrobial peptide studied here is an antimicrobial peptide from skin secretion of toad, Bombina maxima. It is a novel maximin H peptide which is produced through posttranslational modification of a precursor protein, and was named Maximin H5.
By analyzing the composition of amino acids, it contains three acidic aspartates, but has no basic amino acids. Based on the previous study, it seemed to be sensitive only to Gram positive bacteria. So far, few acidic antimicrobial peptides were found and little was known about their three-dimensional structures and mechanisms of killing microbes. In order to understand the structure-function relationship of maximin H5, we used NMR spectroscopy and structure calculation techniques to determine its three-dimensional structure and elucidate the bactericidal mechanism from the characteristics of three-dimensional structure.
Estimated the secondary structures from the chemical shift index, we found maximin H5 seemed to have helical structure at C-terminal region, but there is no obvious helical structure existed based on the calculated structure. Moreover, the surface charge of maximin H5 distribution graph showed that there is no amphipathic structure existed. In addition, its overall negative charge made it hard to attach to bacterial membrane. In conclusion, we propose the bactericidal mechanism of maximin H5 may not directly interact with the membrane of bacteria.

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