Vannuffel P, Di Giambattista M, Cocito C
Microbiology and Genetics Unit, University of Louvain Medical School, Brussels, Belgium.
J Biol Chem. 1992 Aug 15;267(23):16114-20.
Synergism of streptogramins A (virginiamycin M, VM) and B (virginiamycin S, VS), peptidyltransferase inhibitors, was explored in EM4/pLC7-21 (wild type) and EM4/pERY (VS-resistant). These bacterial strains contained multicopy plasmids carrying an rrnH operon with wild type (pLC7-21) or mutated (A2058----U transversion) 23 S rRNA gene. Ribosomes with wild type and mutated rRNA were both present in EM4/pERY. The latter particles did not bind VS; in the presence of VM, however, high affinity VS binding occurred. As shown previously, VS protected against chemical reagents certain bases in domain V rRNA and VM in the stems flanking this loop. Differences between wild type and mutant ribosomes were observed: A2058, A2059, A2062, and G2505, protected by VS and ERY in EM4/pLC7-21, were unshielded in EM4/pERY. A2062 was shielded by VM in EM4/pERY, not in EM4/pLC7-21, and G2505 of mutant ribosomes became protected by VS when VM was simultaneously present. Induction by VM of a high affinity VS binding site in VS-sensitive and -resistant ribosomes indicates A2058 mutation to entail a conformational change of this site, which is counteracted by VM fixation. Accessibility of A2062 to chemical reagents (unlike behavior of EM4/pERY and EM4/pLC7-21 in the presence of VM) implies different conformations for wild type and mutant ribosomes.
在EM4/pLC7 - 21（野生型）和EM4/pERY（对维吉尼亚霉素S耐药）中研究了链阳性菌素A（维吉尼亚霉素M，VM）和B（维吉尼亚霉素S，VS）这两种肽基转移酶抑制剂的协同作用。这些细菌菌株含有携带rrnH操纵子的多拷贝质粒，该操纵子带有野生型（pLC7 - 21）或突变型（A2058→U颠换）的23S rRNA基因。EM4/pERY中同时存在具有野生型和突变型rRNA的核糖体。后者的颗粒不结合VS；然而，在VM存在的情况下，会发生高亲和力的VS结合。如先前所示，VS保护V结构域rRNA中的某些碱基免受化学试剂影响，而VM保护该环侧翼茎中的碱基。观察到野生型和突变型核糖体之间的差异：在EM4/pLC7 - 21中受VS和红霉素保护的A2058、A2059、A2062和G2505，在EM4/pERY中未被保护。在EM4/pERY中A2062被VM保护，在EM4/pLC7 - 21中则不然，当同时存在VM时，突变型核糖体的G2505会被VS保护。VM在VS敏感和耐药核糖体中诱导高亲和力VS结合位点，表明A2058突变导致该位点的构象变化，而VM的结合可抵消这种变化。A2062对化学试剂的可及性（与VM存在时EM4/pERY和EM4/pLC7 - 21的行为不同）意味着野生型和突变型核糖体具有不同的构象。
