Institute for Molecular Biosciences, Goethe University, Frankfurt am Main, Germany.
FIERCE, Goethe University, Frankfurt am Main, Germany.
J Microbiol Biotechnol. 2021 May 28;31(5):645-658. doi: 10.4014/jmb.2103.03009.
Porins are essential for the viability of Gram-negative bacteria. They ensure the uptake of nutrients, can be involved in the maintenance of outer membrane integrity and define the antibiotic or drug resistance of organisms. The function and structure of porins in proteobacteria is well described, while their function in photoautotrophic cyanobacteria has not been systematically explored. We compared the domain architecture of nine putative porins in the filamentous cyanobacterium sp. PCC 7120 and analyzed the seven candidates with predicted OprB-domain. Single recombinant mutants of the seven genes were created and their growth capacity under different conditions was analyzed. Most of the putative porins seem to be involved in the transport of salt and copper, as respective mutants were resistant to elevated concentrations of these substances. In turn, only the mutant of was less sensitive to elevated zinc concentrations, while mutants of , and were resistant to high manganese concentrations. Notably the mutant of shows a high sensitivity against harmful compounds, which is indicative for a function related to the maintenance of outer membrane integrity. Moreover, the mutant of exhibited a phenotype which suggests either a higher nitrate demand or an inefficient nitrogen fixation. The dependency of porin membrane insertion on Omp85 proteins was tested exemplarily for Alr4550, and an enhanced aggregation of Alr4550 was observed in two mutants. The comparative analysis of porin mutants suggests that the proteins in parts perform distinct functions related to envelope integrity and solute uptake.
孔蛋白对于革兰氏阴性菌的生存至关重要。它们确保了营养物质的摄取，可以参与维持外膜的完整性，并决定了生物体对抗生素或药物的耐药性。变形菌中孔蛋白的功能和结构已经得到了很好的描述，而它们在光自养蓝藻中的功能尚未得到系统的探索。我们比较了丝状蓝藻 sp. PCC 7120 中 9 种假定孔蛋白的结构域架构，并分析了具有预测的 OprB 结构域的 7 个候选蛋白。创建了这 7 个基因的单个重组突变体，并分析了它们在不同条件下的生长能力。大多数假定的孔蛋白似乎参与了盐和铜的运输，因为相应的突变体对这些物质的高浓度具有抗性。反过来，只有突变体对高浓度锌的敏感性降低，而突变体和对高浓度锰具有抗性。值得注意的是，突变体对有害物质表现出高度的敏感性，这表明其与维持外膜完整性的功能有关。此外，突变体的表型表明其对硝酸盐的需求较高，或者固氮效率较低。我们以 Alr4550 为例测试了孔蛋白插入膜的依赖性与 Omp85 蛋白有关，并且在两个突变体中观察到 Alr4550 的聚集增强。孔蛋白突变体的比较分析表明，这些蛋白在某些方面执行着与 envelope integrity 和溶质摄取相关的不同功能。
