Tytler E M, Anantharamaiah G M, Walker D E, Mishra V K, Palgunachari M N, Segrest J P
Department of Medicine, University of Alabama, Birmingham Medical Center 35294, USA.
Biochemistry. 1995 Apr 4;34(13):4393-401. doi: 10.1021/bi00013a031.
Magainins and mastoparans are examples of peptide antibiotics and peptide venoms, respectively. They have been grouped together as class L amphipathic helixes [Segrest, J.P., et al. (1990) Proteins 8, 103-117] because of similarities in the distribution of Lys residues along the polar face of the helix. Class L venoms lyse both eukaryotic and prokaryotic cells whereas class L antibiotics specifically lyse bacteria. The structural basis for the specificity of class L antibiotics is not well understood. Sequence analysis showed that class L antibiotics have a Glu residue on the nonpolar face of the amphipathic helix; this is absent from class L venoms. We synthesized three model class L peptides with or without Glu on the nonpolar face: 18LMG (LGSIWKFIKAFVGGIKKF), [E14]18LMG and [G5,E14]18LMG. Hemolysis, bacteriolysis, and bacteriostasis studies using these peptides showed that the specificity of lysis is due to both the presence of a Glu residue on the nonpolar face of the helix and the bulk of the nonpolar face. Studies using large unilamellar phospholipid vesicles showed that the inclusion of cholesterol greatly inhibited leakage by the two Glu-containing peptides. These results cannot be attributed to changes in the phase behavior of the lipids caused by the inclusion of cholesterol or to differences in the secondary structure of the peptides. These results suggest that eukaryotic cells are resistant to lysis by magainins because of peptide-cholesterol interactions in their membranes that inhibit the formation of peptide structures capable of lysis, perhaps by hydrogen bonding between Glu and cholesterol. Bacterial membranes, lacking cholesterol, are susceptible to lysis by magainins.
蛙皮素和mastoparans分别是肽抗生素和肽毒素的例子。由于沿着螺旋极面的赖氨酸残基分布相似，它们被归为L类两亲性螺旋[Segrest, J.P.,等人(1990)蛋白质8, 103 - 117]。L类毒素可裂解真核细胞和原核细胞，而L类抗生素则特异性裂解细菌。L类抗生素特异性的结构基础尚不清楚。序列分析表明，L类抗生素在两亲性螺旋的非极面上有一个谷氨酸残基；L类毒素中没有这个残基。我们合成了三种在非极面上有或没有谷氨酸的L类模型肽：18LMG (LGSIWKFIKAFVGGIKKF)、[E14]18LMG和[G5,E14]18LMG。使用这些肽进行的溶血、细菌裂解和抑菌研究表明，裂解的特异性是由于螺旋非极面上存在谷氨酸残基以及非极面的大小。使用大单层磷脂囊泡的研究表明，加入胆固醇极大地抑制了两种含谷氨酸肽引起的泄漏。这些结果不能归因于加入胆固醇导致的脂质相行为变化或肽二级结构的差异。这些结果表明，真核细胞对蛙皮素裂解具有抗性，是因为其膜中的肽 - 胆固醇相互作用抑制了能够裂解的肽结构的形成，可能是通过谷氨酸和胆固醇之间的氢键作用。缺乏胆固醇的细菌膜易被蛙皮素裂解。
