Depardieu Florence, Bonora Maria Grazia, Reynolds Peter E, Courvalin Patrice
Unité des Agents Antibactériens, Institut Pasteur, 25 rue du Docteur Roux, 75724 Paris, Cedex 15, France.
Mol Microbiol. 2003 Nov;50(3):931-48. doi: 10.1046/j.1365-2958.2003.03737.x.
Acquired VanG-type resistance to vancomycin (MIC = 16 micro g ml(-1)) but susceptibility to teicoplanin in Enterococcus faecalis BM4518 and WCH9 is due to the inducible synthesis of peptidoglycan precursors ending in d-alanine-d-serine. The vanG cluster, assigned to a chromosomal location, was composed of genes recruited from various van operons. The 3' end encoded VanG, a d-Ala:d-Ser ligase, VanXY(G), a putative bifunctional d,d-peptidase and VanT(G), a serine racemase: VanG and VanT(G) were implicated in the synthesis of d-Ala:d-Ser as in VanC- and VanE-type strains. Upstream from the structural genes for these proteins were vanW(G) with unknown function and vanY(G) containing a frameshift mutation which resulted in premature termination of the encoded protein and accounted for the lack of UDP-MurNAc-tetrapeptide in the cytoplasm. Without the frameshift mutation, VanY(G) had homology with Zn2+ dependent d,d-carboxypeptidases. The 5' end of the gene cluster contained three genes vanU(G), vanR(G) and vanS(G) encoding a putative regulatory system, which were co-transcribed constitutively from the PY(G) promoter, whereas transcription of vanY(G),W(G),G,XY(G),T(G) was inducible and initiated from the P(YG) promoter. Transfer of VanG-type glycopeptide resistance to E. faecalis JH2-2 was associated with the movement, from chromosome to chromosome, of genetic elements of c. 240 kb carrying also ermB-encoded erythromycin resistance. Sequence determination of the flanking regions of the vanG cluster in donor and transconjugants revealed the same 4 bp direct repeats and 22 bp imperfect inverted repeats that delineated the large element.
粪肠球菌BM4518和WCH9对万古霉素获得性VanG型耐药（MIC = 16 μg/ml(-1)）但对替考拉宁敏感，这是由于以d-丙氨酸-d-丝氨酸结尾的肽聚糖前体的可诱导合成。定位于染色体位置的vanG基因簇由从各种van操纵子募集的基因组成。3'端编码VanG，一种d-Ala:d-Ser连接酶，VanXY(G)，一种推定的双功能d,d-肽酶和VanT(G)，一种丝氨酸消旋酶：VanG和VanT(G)与VanC型和VanE型菌株中d-Ala:d-Ser的合成有关。这些蛋白质的结构基因上游是功能未知的vanW(G)和含有移码突变的vanY(G)，该突变导致编码蛋白的过早终止，并解释了细胞质中缺乏UDP-MurNAc-四肽的原因。没有移码突变时，VanY(G)与锌离子依赖性d,d-羧肽酶具有同源性。基因簇的5'端包含三个编码推定调节系统的基因vanU(G)、vanR(G)和vanS(G)，它们从PY(G)启动子组成性共转录，而vanY(G)、W(G)、G、XY(G)、T(G)的转录是可诱导的，并从P(YG)启动子开始。VanG型糖肽耐药性向粪肠球菌JH2-2的转移与约240 kb的遗传元件从一条染色体转移到另一条染色体有关，该遗传元件还携带ermB编码的红霉素耐药性。供体和转接合子中vanG基因簇侧翼区域的序列测定揭示了界定大元件的相同4 bp直接重复序列和22 bp不完全反向重复序列。
