Burgos Raul, Pich Oscar Q, Ferrer-Navarro Mario, Baseman Joel B, Querol Enrique, Piñol Jaume
Institut de Biotecnologia i Biomedicina and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain.
J Bacteriol. 2006 Dec;188(24):8627-37. doi: 10.1128/JB.00978-06. Epub 2006 Oct 6.
Mycoplasma genitalium is a human pathogen that mediates cell adhesion by a complex structure known as the attachment organelle. This structure is composed of cytadhesins and cytadherence-associated proteins, but few data are available about the specific role of these proteins in M. genitalium cytadherence. We have deleted by homologous recombination the mg191 and mg192 genes from the MgPa operon encoding the P140 and P110 cytadhesins. Molecular characterization of these mutants has revealed a reciprocal posttranslational stabilization between the two proteins. Loss of either P140 or P110 yields a hemadsorption-negative phenotype and correlates with decreased or increased levels of cytoskeleton-related proteins MG386 and DnaK, respectively. Scanning electron microscopy analysis reveals the absolute requirement of P140 and P110 for the proper development of the attachment organelle. The phenotype described for these mutants resembles that of the spontaneous class I and class II cytadherence-negative mutants [G. R. Mernaugh, S. F. Dallo, S. C. Holt, and J. B. Baseman, Clin. Infect. Dis. 17(Suppl. 1):S69-S78, 1993], whose genetic basis remained undetermined until now. Complementation assays and sequencing analysis demonstrate that class I and class II mutants are the consequence of large deletions affecting the mg192 and mg191-mg192 genes, respectively. These deletions originated from single-recombination events involving sequences of the MgPa operon and the MgPa island located immediately downstream. We also demonstrate the translocation of MgPa sequences to a particular MgPa island by double-crossover events. Based on these observations, we propose that in addition to being a source of antigenic variation, MgPa islands could be also involved in a general phase variation mechanism switching on and off, in a reversible or irreversible way, the adhesion properties of M. genitalium.
生殖支原体是一种人类病原体，它通过一种称为附着细胞器的复杂结构介导细胞黏附。该结构由细胞黏附素和细胞黏附相关蛋白组成，但关于这些蛋白在生殖支原体细胞黏附中的具体作用，目前可用的数据很少。我们通过同源重组从编码P140和P110细胞黏附素的MgPa操纵子中删除了mg191和mg192基因。对这些突变体的分子特征分析揭示了这两种蛋白之间相互的翻译后稳定作用。P140或P110的缺失均产生血细胞吸附阴性表型，分别与细胞骨架相关蛋白MG386水平降低或DnaK水平升高相关。扫描电子显微镜分析表明，P140和P110是附着细胞器正常发育的绝对必需条件。这些突变体所描述的表型类似于自发的I类和II类细胞黏附阴性突变体[G. R. Mernaugh, S. F. Dallo, S. C. Holt, and J. B. Baseman, Clin. Infect. Dis. 17(Suppl. 1):S69 - S78, 1993]，其遗传基础至今仍未确定。互补试验和测序分析表明，I类和II类突变体分别是影响mg192和mg191 - mg192基因的大片段缺失的结果。这些缺失源于涉及MgPa操纵子序列和紧邻下游的MgPa岛序列的单重组事件。我们还通过双交换事件证明了MgPa序列向特定MgPa岛的易位。基于这些观察结果，我们提出，MgPa岛除了是抗原变异的来源外，还可能参与一种一般的相变机制，以可逆或不可逆的方式开启和关闭生殖支原体的黏附特性。
