Data_Sheet_1_Identifying a Molecular Mechanism That Imparts Species-Specific Toxicity to YoeB Toxins.pdf

The ribosome-dependent E. coli (Ec) mRNase toxin YoeB has been demonstrated to protect cells during thermal stress. Agrobacterium tumefaciens (At), a plant pathogen, also encodes a YoeB toxin. Initial studies indicated that AtYoeB does not impact the growth of Ec, but its expression is toxic to the native host At. The current work examines this species-specific effect. We establish the highly similar structure and function of Ec and AtYoeB toxins, including the ability of the AtYoeB toxin to inhibit Ec ribosomes in vitro. Comparison of YoeB sequences and structures highlights a four-residue helix between β-strands 2 and 3 that interacts with mRNA bases within the ribosome. This helix sequence is varied among YoeB toxins, and this variation correlates with bacterial classes of proteobacteria. When the four amino acid sequence of this helix is transplanted from EcYoeB onto AtYoeB, the resulting chimera gains toxicity to Ec cells and lessens toxicity to At cells. The reverse is also true, such that EcYoeB with the AtYoeB helix sequence is less toxic to Ec and gains toxicity to At cultures. We suggest this helix sequence directs mRNA sequence-specific degradation, which varies among proteobacterial classes, and thus controls growth inhibition and YoeB toxicity.

依赖核糖体的大肠杆菌（E. coli，缩写Ec）mRNA特异性核糖核酸酶（mRNase）毒素YoeB已被证实可在热应激条件下保护细胞。植物病原菌根癌农杆菌（Agrobacterium tumefaciens，缩写At）同样编码YoeB毒素。前期研究发现，AtYoeB不会影响Ec的生长，但其表达会对天然宿主At产生毒性。本研究针对这一物种特异性效应展开探究。我们证实，Ec与AtYoeB毒素在结构与功能上高度相似，其中包括AtYoeB毒素在体外抑制Ec核糖体的能力。对YoeB序列与结构的比对分析显示，其β折叠链2与3之间存在一段由四个氨基酸残基构成的螺旋区，该区域可与核糖体中的mRNA碱基相互作用。此类螺旋序列在不同YoeB毒素中存在序列差异，且该差异与变形菌门（Proteobacteria）的细菌类群具有相关性。当将EcYoeB的该四段氨基酸螺旋序列移植至AtYoeB中时，所获得的嵌合毒素获得了对Ec细胞的毒性，同时减弱了对At细胞的毒性。反之亦然：携带AtYoeB螺旋序列的EcYoeB对Ec细胞的毒性减弱，同时获得了对At培养物的毒性。我们推测，该螺旋序列可介导mRNA序列特异性降解（此类降解在不同变形菌门类群中存在差异），进而调控生长抑制效应与YoeB毒素的毒性强度。