Instituto de Biotecnología, Instituto Nacional de Tecnología Agropecuaria, CICVyA-INTA, Buenos Aires, Argentina.
PLoS One. 2012;7(3):e33605. doi: 10.1371/journal.pone.0033605. Epub 2012 Mar 15.
The twin-arginine translocation (Tat) pathway exports fully folded proteins out of the cytoplasm of Gram-negative and Gram-positive bacteria. Although much progress has been made in unraveling the molecular mechanism and biochemical characterization of the Tat system, little is known concerning its functionality and biological role to confer adaptive skills, symbiosis or pathogenesis in the α-proteobacteria class. A comparative genomic analysis in the α-proteobacteria class confirmed the presence of tatA, tatB, and tatC genes in almost all genomes, but significant variations in gene synteny and rearrangements were found in the order Rickettsiales with respect to the typically described operon organization. Transcription of tat genes was confirmed for Anaplasma marginale str. St. Maries and Brucella abortus 2308, two α-proteobacteria with full and partial intracellular lifestyles, respectively. The tat genes of A. marginale are scattered throughout the genome, in contrast to the more generalized operon organization. Particularly, tatA showed an approximately 20-fold increase in mRNA levels relative to tatB and tatC. We showed Tat functionality in B. abortus 2308 for the first time, and confirmed conservation of functionality in A. marginale. We present the first experimental description of the Tat system in the Anaplasmataceae and Brucellaceae families. In particular, in A. marginale Tat functionality is conserved despite operon splitting as a consequence of genome rearrangements. Further studies will be required to understand how the proper stoichiometry of the Tat protein complex and its biological role are achieved. In addition, the predicted substrates might be the evidence of role of the Tat translocation system in the transition process from a free-living to a parasitic lifestyle in these α-proteobacteria.
双精氨酸转运（Tat）途径将完全折叠的蛋白质从革兰氏阴性和革兰氏阳性细菌的细胞质中输出。尽管在揭示 Tat 系统的分子机制和生化特性方面已经取得了很大进展，但对于其功能及其在α-变形菌中的适应性技能、共生或发病机制的生物学作用知之甚少。α-变形菌中的比较基因组分析证实，tatA、tatB 和 tatC 基因几乎存在于所有基因组中，但在立克次氏体目中，发现基因同线性和重排存在显著差异，与通常描述的操纵子组织不同。对具有完全和部分细胞内生活方式的两种α-变形菌，边缘无浆体菌株 St. Maries 和布鲁氏菌 abortus 2308，证实了 tat 基因的转录。与 tatB 和 tatC 相比，边缘无浆体的 tatA 基因在基因组中散布，而不是更普遍的操纵子组织。特别是，tatA 的 mRNA 水平相对于 tatB 和 tatC 增加了约 20 倍。我们首次在布鲁氏菌 abortus 2308 中证明了 Tat 的功能，并证实了边缘无浆体的功能保守性。我们首次描述了 Anaplasmataceae 和 Brucellaceae 家族中的 Tat 系统。特别是，尽管由于基因组重排导致操纵子分裂，但边缘无浆体中的 Tat 功能仍然保守。需要进一步的研究来了解 Tat 蛋白复合物的适当化学计量及其生物学作用是如何实现的。此外，预测的底物可能是 Tat 易位系统在这些α-变形菌中从自由生活到寄生生活过渡过程中发挥作用的证据。
