Di Giambattista M, Engelborghs Y, Nyssen E, Clays K, Cocito C
Microbiology and Genetics Unit, University of Louvain Medical School, Brussels, Belgium.
Biochemistry. 1991 Jul 23;30(29):7277-82. doi: 10.1021/bi00243a033.
Type B streptogramins, such as virginiamycin S (VS), are cyclic hexadepsipeptides, inhibiting protein synthesis in prokaryotes. L-Thr connects a 3-hydroxypicolinyl residue (3-OH-Pic) to the peptide lactone ring. The fluorescence intensity of 3-OH-Pic is strongly increased by chelation to alkaline earth cations or binding to ribosomes. Similar behavior of the ribosome-VS complex and the VS-Mg chelate provides strong evidence for the presence of a VS-Mg chelate within the ribosomal binding site. Different models involving the ribosome binding of either members of the VS-Mg2+ chelate or both have been tested by fluorescence lifetime measurements, equilibrium titrations, and stopped-flow spectrofluorometry. Our data strongly suggest that (a) the interaction between VS and the ribosome is partly provided by a salt bridge between suitable acceptor atoms of the ribosome and the 3-OH-Pic residue, (b) Mg2+ can be exchanged by Mn2+ without dissociation of the ribosome-VS complex, (c) Mg2+ coordinates to the negative form of the 3-OH-Pic residue, probably via an interaction with the phenolate oxygen and the amide carboxyl group, and (d) the picolinyl residue is essential for the biological activity, as indicated by the lack of activity when the latter is replaced by a serine derivative.
B型链阳菌素，如维吉尼亚霉素S（VS），是环状六聚脂肽，可抑制原核生物中的蛋白质合成。L-苏氨酸将一个3-羟基吡啶基残基（3-OH-Pic）连接到肽内酯环上。通过与碱土金属阳离子螯合或与核糖体结合，3-OH-Pic的荧光强度会显著增加。核糖体-VS复合物和VS-Mg螯合物的类似行为为核糖体结合位点内存在VS-Mg螯合物提供了有力证据。通过荧光寿命测量、平衡滴定和停流荧光光谱法测试了涉及VS-Mg2+螯合物成员之一或两者与核糖体结合的不同模型。我们的数据强烈表明：（a）VS与核糖体之间的相互作用部分是由核糖体合适的受体原子与3-OH-Pic残基之间的盐桥提供的；（b）Mg2+可以被Mn2+取代而不使核糖体-VS复合物解离；（c）Mg2+可能通过与酚氧和酰胺羧基的相互作用与3-OH-Pic残基的负性形式配位；（d）吡啶基残基对生物活性至关重要，当后者被丝氨酸衍生物取代时缺乏活性就表明了这一点。
