细菌微室

Bacterial microcompartments

长期以来,人们认为细菌的细胞没有细胞器,但是最近20年细菌微室的研究颠覆了这一传统观点.微室是细菌的细胞器,由壳蛋白和酶蛋白通过自组织形成.细菌微室与病毒在外观上很像,为100~200 nm的多面体.细菌微室的系统性研究源于沙门氏菌1,2-丙二醇分解代谢途径的研究.该途径相关基因形成pdu操纵子,pdu操纵子中除了酶蛋白外还有一些结构基因编码微室壳蛋白.细菌微室的生理功能是由蛋白质壳形成一个防止分子扩散的屏障,将内部环境与细胞质进行物理隔离,使得含有易挥发或有毒化合物的代谢反应容易进行.细菌微室在细菌中广泛分布,种类繁多,目前已经在分布于45个门的细菌中发现68种微室基因簇.细菌微室的生理功能具有高度多样性,在二氧化碳固定和多种化合物分解代谢中具有重要生理功能.本文主要就细菌微室的结构、生理功能、主要类别以及细菌微室在生物工程领域的应用前景等进行介绍.

Traditionally,bacteria were considered primitive organisms that lack intracellular organization.However,this knowledge was overturned by studies that showed bacteria have a high level of organization including research on bacterial microcompartments.Microcompartments are self-assembling organelles composed of a protein shell,and internal enzymes encapsulated by the shell.The overall morphology of bacterial microcompartments is similar to viruses.They are polyhedral in shape and about 100 to 200 nm in size.The common feature of bacterial microcompartments is that they use a protein shell as a diffusion barrier to help channel toxic or volatile pathway intermediates to the next pathway enzyme.Gene clusters of bacterial microcompartments are widespread,and their specific physiological roles are diverse.68 types were found in the genome of bacteria across 45 phyla.However,the functions of many types of bacterial microcompartments remain unclear,and only several types have been characterized experimentally.One of the beststudied microcompartments is used for 1,2-propanediol catabolism in Salmonella typhimurium.Genes encoding enzymes that are responsible for 1,2-propanediol catabolism and shell proteins form a pdu operon.Enzymes and shell proteins of pdu operon form a Propanediol utilization(Pdu)microcompartment.1,2-Propanediol is transported into the lumen of the microcompartment,where it is converted to propionaldehyde by propanediol dehydratase.Propionaldehyde is a toxic chemical and high levels of propionaldehyde inhibit the activity of the cell.The shell of the Pdu microcompartment prevents the propionaldehyde transported into the cytoplasm and reduces its toxicity to the cell.Propionaldehyde is converted to propanol,a less toxic chemical,and finally transported into the cytoplasm.The disruption of the Pdu microcompartment increases propionaldehyde levels in the culture broth,and slows the growth of cells.The carboxysome microcompartment is another type of highly investigated microcompartment.It is used to enhance autotrophic CO_(2)fixation and is found in nearly all cyanobacteria and some chemoautotrophs.Bicarbonate crosses the protein shell of the carboxysome and enters the lumen,where bicarbonate is converted to CO_(2).The protein shell of the carboxysome helps to maintain a high local concentration of CO_(2)by inhibiting its outward diffusion.If the shell of the carboxysome is disrupted,cells are unable to grow autotrophically at atmospheric CO_(2).levels.Besides these two types of microcompartments,the ethanolamine utilization(Eut)microcompartment,glycyl-radical propanediol(Grp)microcompartment,choline utilization(Cut)microcompartment,Planctomycete and Verrucomicrobia(PV)microcompartment,taurine metabolism microcompartment,and ethanol utilization(Eut)microcompartment are microcompartments whose specific function is known.Bacterial microcompartments are interesting structures,and they have potential applications in biomedicine and biotechnology.Some heterologous pathways have been encapsulated into microcompartments and shown potential biotechnology advantages.Research on bacterial microcompartments is in its infancy,but these tiny organelles have big potential.