Samen Ulrike, Gottschalk Birgit, Eikmanns Bernhard J, Reinscheid Dieter J
Department of Microbiology and Biotechnology, University of Ulm, D-89069 Ulm, Germany.
J Bacteriol. 2004 Mar;186(5):1398-408. doi: 10.1128/JB.186.5.1398-1408.2004.
Streptococcus agalactiae is a major cause of invasive infections in human newborns. To satisfy its growth requirements, S. agalactiae takes up 9 of the 20 proteinogenic amino acids from the environment. Defined S. agalactiae mutants in one or several of four putative peptide permease systems were constructed and tested for peptide uptake, growth in various media, and expression of virulence traits. Oligopeptide uptake by S. agalactiae was shown to be mediated by the ABC transporter OppA1-F, which possesses two substrate-binding proteins (OppA1 and OppA2) with overlapping substrate specificities. Dipeptides were found to be taken up in parallel by the oligopeptide permease OppA1-F, by the dipeptide ABC transporter DppA-E, and by the dipeptide symporter DpsA. Reverse transcription-PCR analysis revealed a polycistronic organization of the genes oppA1-F and dppA-E and a monocistronic organization of dpsA in S. agalactiae. The results of quantitative real-time PCR revealed a medium-dependent expression of the operons dppA-E and oppA1-F in S. agalactiae. Growth of S. agalactiae in human amniotic fluid was shown to require an intact dpsA gene, indicating an important role of DpsA during the infection of the amniotic cavity by S. agalactiae. Deletion of the oppB gene reduced the adherence of S. agalactiae to epithelial cells by 26%, impaired its adherence to fibrinogen and fibronectin by 42 and 33%, respectively, and caused a 35% reduction in expression of the fbsA gene, which encodes a fibrinogen-binding protein in S. agalactiae. These data indicate that the oligopeptide permease is involved in modulating virulence traits and virulence gene expression in S. agalactiae.
无乳链球菌是人类新生儿侵袭性感染的主要病因。为满足其生长需求，无乳链球菌从环境中摄取20种蛋白质氨基酸中的9种。构建了四个假定的肽通透酶系统中一个或几个的特定无乳链球菌突变体，并对其进行肽摄取、在各种培养基中的生长以及毒力性状表达的测试。结果表明，无乳链球菌的寡肽摄取由ABC转运蛋白OppA1-F介导，该转运蛋白拥有两个底物结合蛋白（OppA1和OppA2），其底物特异性重叠。发现二肽可由寡肽通透酶OppA1-F、二肽ABC转运蛋白DppA-E和二肽同向转运蛋白DpsA并行摄取。逆转录PCR分析揭示了无乳链球菌中oppA1-F和dppA-E基因的多顺反子组织以及dpsA的单顺反子组织。定量实时PCR结果显示，无乳链球菌中dppA-E和oppA1-F操纵子的表达呈培养基依赖性。结果表明，无乳链球菌在人羊水中的生长需要完整的dpsA基因，这表明DpsA在无乳链球菌感染羊膜腔过程中起重要作用。oppB基因的缺失使无乳链球菌对上皮细胞的黏附减少了26%，对纤维蛋白原和纤连蛋白的黏附分别受损42%和33%，并导致编码无乳链球菌纤维蛋白原结合蛋白的fbsA基因表达降低35%。这些数据表明，寡肽通透酶参与调节无乳链球菌的毒力性状和毒力基因表达。
