Mastoparan B (MPB-NH2)從胡蜂毒液分離出的抗菌胜肽，由14 個 胺基酸所組成並含有多個正電性胺基酸殘基與碳端修飾為NH2。文 獻指出2 號位置的lysine 與九號位置的tryptophan 對MPB-NH2 有重 要的影響。我們分別用asparagine 與tyrosine 置換上述殘基，形成 Y9-MPB-NH2 及N2Y9-MPB-NH2 的MPB-NH2 衍生物，並使用SDS 與TFE 兩種不同溶液環境在溫度310 K 來探討MPB-NH2 與其衍生物 之結構、動力學行為與抗菌活性之間的關係。 抗菌實驗結果表示其抑菌活性由高至低分別為MPB-NH2、Y9- MPB-NH2 與N2Y9-MPB-NH2。CD 實驗觀察到MPB-NH2 及其衍生物 在水中為無序纏繞的構形，在30 % TFE 溶液中與SDS 微胞中形成α 螺旋結構。但在SDS 微胞中，MPB-NH2 與Y9-MPB-NH2 的α 螺旋含 量均比在30 % TFE 溶液中來得高。從Model-free 分析MPB 胜肽在 TFE 水溶液的動力學行為發現，N2Y9-MPB-NH2 在N 端的動性較另 外兩條胜肽穩定。擴散實驗表示Y9-MPB-NH2 與N2Y9-MPB-NH2 在 TFE 310 K 具有相似的寡聚現象，這兩條胜肽分子間相互作用的能量 也相似。再比較在TFE 與SDS 環境改變時胜肽的化學位移變化，我 們觀察到Y9-MPB-NH2 與N2Y9-MPB-NH2 的N端NH化學位移有不 同的表現，可能是N 端電荷與膜作用改變所導致。 MPB 抑菌活性的表現受到N 端與C 端的正電荷Lys 殘基與膜結 合能力的影響，動性較大的N 端在與膜結合時，誘發N 端helix 的形 成，產生適當的構形與膜接觸，以利疏水殘基的插入。而兩親性螺 旋，其疏水性一側的殘基，如Trp，其疏水性將會影響胜肽插入膜疏 水核心的能力。 Mastoparan B (MPB) is an antimicrobial peptide that was isolated from the hornet (Vespa basalis) venom. It’s composed of 14 amino acids, containing multiple positive charge residues and amidated C-terminus. Studies have suggested that the lysine at position 2 and the tryptophan at position 9 are important for the activities of MPB. To probe their role for structure and activity, we synthesized three peptides, MPB, Y9 (mutated at position 2 with asparagines) and N2Y9 (mutated at position 2 and 9 with asparagines and tyrosine, respectively). We investigated their antimicrobial activity, structure and dynamics at 310 K in both 30%/70% TFE/H2O and SDS micell solutions. Antimicrobial activity of the peptides, in sequence from the highest to the lowest, is showed as MPB, Y9 and N2Y9. Circular dichroism (CD) spectra indicated that the peptides adopt random coil conformation in water and α-helical structure in TFE and SDS micell solutions. In TFE, the N-terminal structures of MPB and Y9 are demonstrated more diverged and flexible than that of N2Y9. However, MPB and Y9 form longer and more stable helical structures in SDS environment. It is suggested that the affinity of binding with SDS for MPB and Y9 is higher than for N2Y9. The diffusion studies showed that the oligomerized behaviors of Y9 and N2Y9 are similar in TFE. It indicates that these two peptides with similar energetics in intermolecular interactions. As changed from TFE to SDS environment, the change profile of NH chemical shifts in N-terminal is quite different between Y9 and N2Y9.It may contribute to the consequence of N-terminal charge interacted with membrane. Antibacterial activity of MPB and its binding ability with membrane are affected by the positive charge residue Lys at N-terminal and C-terminal. The flexible N-terminal when contact with membrane will form active conformation to facilitate the insertion of hydrophobic residues into membrane. Trp as well as the hydrophobic residues on one side of the amphipathic helix can affect the capacity of peptide into hydrophobic membrane core.