Melectin: a novel antimicrobial peptide from the venom of the cleptoparasitic bee Melecta albifrons

A novel antimicrobial peptide designated melectin was isolated from the venom of the cleptoparasitic bee Melecta albifrons. Its primary sequence was established as H-Gly-Phe-Leu-Ser-Ile-Leu-Lys-Lys-Val-Leu-Pro-Lys-Val-Met-Ala-His-Met-Lys-NH(2) by Edman degradation and ESI-QTOF mass spectrometry. Synthetic melectin exhibited antimicrobial activity against both gram-positive and -negative bacteria and it degranulated rat peritoneal mast cells, but its hemolytic activity was low. The CD spectra of melectin measured in the presence of trifluoroethanol and sodium dodecyl sulfate showed a high content alpha-helices, which indicates that melectin can adopt an amphipathic alpha-helical secondary structure in an anisotropic environment such as the bacterial cell membrane. To envisage the role of the proline residue located in the middle of the peptide chain on biological activity and secondary structure, we prepared several melectin analogues in which the Pro11 residue was either replaced by other amino acid residues or was omitted. The results of biological testing suggest that a Pro kink in the alpha-helical structure of melectin plays an important role in selectivity for bacterial cells. In addition, a series of N- and C-terminal-shortened analogues was synthesized to examine which region of the peptide is related to antimicrobial activity.     

聚氧丙烯链对延展型表面活性剂的双亲性贡献

以天然月桂醇为原料,采用丙氧基化反应、硫酸酯化反应和中和反应合成了系列月桂基聚氧丙烯醚硫酸钠(SLP_pS,依据月桂醇与环氧丙烷物质的量比计算得到p=3、6、9),采用红外和核磁氢谱对其进行了结构表征。考察了SLP_pS的表面张力、泡沫、乳化、润湿、去污、临界胶束温度和钙离子抗性等界面和胶束溶液性质,并与两种传统表面活性剂十二烷基硫酸钠(SDS)和月桂基聚氧乙烯醚硫酸钠(SLE_3S)对比,突显聚氧丙烯(PPO)链对延展型表面活性剂性质的影响。结果表明,PPO链不仅为SLP_pS分子提供疏水贡献,使SLP_pS的表面张力降低至32.1 mN/m以下,并使其临界胶束浓度低至1.0×10~(-4) mol/L数量级,同时产生了优于SDS和SLE_3S的乳化、润湿和去污能力,而且提供弱的极性贡献,产生低于0℃的临界胶束温度和高于SDS约30倍的钙离子抗性。SLP_pS的优异性质使其适用于个人护理及家用清洁产品中。     

Membrane Affinity of Platensimycin and Its Dialkylamine Analogs

Membrane permeability is a desired property in drug design, but there have been difficulties in quantifying the direct drug partitioning into native membranes. Platensimycin (PL) is a new promising antibiotic whose biosynthetic production is costly. Six dialkylamine analogs of PL were synthesized with identical pharmacophores but different side chains; five of them were found inactive. To address the possibility that their activity is limited by the permeation step, we calculated polarity, measured surface activity and the ability to insert into the phospholipid monolayers. The partitioning of PL and the analogs into the cytoplasmic membrane of E. coli was assessed by activation curve shifts of a re-engineered mechanosensitive channel, MscS, in patch-clamp experiments. Despite predicted differences in polarity, the affinities to lipid monolayers and native membranes were comparable for most of the analogs. For PL and the di-myrtenyl analog QD-11, both carrying bulky sidechains, the affinity for the native membrane was lower than for monolayers (half-membranes), signifying that intercalation must overcome the lateral pressure of the bilayer. We conclude that the biological activity among the studied PL analogs is unlikely to be limited by their membrane permeability. We also discuss the capacity of endogenous tension-activated channels to detect asymmetric partitioning of exogenous substances into the native bacterial membrane and the different contributions to the thermodynamic force which drives permeation.