Michael Smith Laboratories, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Michael Smith Laboratories, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
J Mol Biol. 2019 Mar 15;431(6):1172-1185. doi: 10.1016/j.jmb.2019.01.041. Epub 2019 Feb 13.
Genetic variation among orthologous genes has been largely formed through neutral genetic drift while maintaining the functional role of these genes. However, because the evolution of gene occurs in the context of each host organism, their sequence changes are also associated with adaptation to a specific environment. Thus, genetic variation can create critical phenotypic variation, particularly when genes are transferred to a new host by horizontal gene transfer. Unveiling "hidden phenotypic variation" is particularly important for genes that confer resistance to antibiotics. However, our understanding of the molecular mechanisms that underlie phenotypic variation remains limited. Here we sought to determine the extent of phenotypic variation in the B1 metallo-β-lactamase (MBL) family and its molecular basis by systematically characterizing eight MBL orthologs, including NDM-1 and VIM-2 and IMP-1. We found that these MBLs confer diverse levels of resistance. The phenotypic variation cannot be explained by variation in catalytic efficiency alone; rather, it is the combination of the catalytic efficiency and abundance of functional periplasmic enzyme that best predicts the observed variation in resistance. The level of functional periplasmic expression varied dramatically between MBL orthologs. This was the result of changes at multiple levels of each ortholog's: (1) quantity of mRNA, (2) amount of MBL expressed, and (3) efficacy of functional enzyme translocation to the periplasm. Overall, it is the interaction between each gene and the host's underlying cellular processes (transcription, translation, and translocation) that determines MBL genetic incompatibility through horizontal gene transfer. These host-specific processes may constrain the effective spread and deployment of MBLs to certain host species and could explain the current observed distribution bias.
基因在保持功能的同时，通过中性遗传漂变在同源基因之间产生了大量的变异。然而，由于基因的进化发生在每个宿主生物体的背景下，它们的序列变化也与适应特定环境有关。因此，遗传变异可以产生关键的表型变异，特别是当基因通过水平基因转移转移到新的宿主时。揭示“隐藏的表型变异”对于赋予抗生素抗性的基因尤为重要。然而，我们对表型变异的分子机制的理解仍然有限。在这里，我们通过系统地表征包括 NDM-1 和 VIM-2 以及 IMP-1 在内的 8 个 MBL 同源物，旨在确定 B1 金属-β-内酰胺酶 (MBL) 家族的表型变异程度及其分子基础。我们发现这些 MBL 赋予了不同程度的抗性。表型变异不能仅用催化效率的变化来解释; 相反，是催化效率和功能性周质酶的丰度的结合，最好地预测了观察到的抗性变化。功能性周质表达水平在 MBL 同源物之间差异显著。这是由于每个同源物的多个水平发生了变化：（1）mRNA 的数量，（2）表达的 MBL 数量，以及（3）功能性酶向周质转运的效率。总的来说，是每个基因与宿主潜在的细胞过程（转录、翻译和转运）之间的相互作用决定了 MBL 通过水平基因转移的遗传不兼容性。这些宿主特异性过程可能限制了 MBL 在某些宿主物种中的有效传播和部署，并可以解释当前观察到的分布偏差。
