Department of Chemistry, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
Physical Biosciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
J Am Chem Soc. 2016 Apr 27;138(16):5262-70. doi: 10.1021/jacs.5b11734. Epub 2016 Jan 11.
Bacterial microcompartments (BMCs) are self-assembling organelles composed of a selectively permeable protein shell and encapsulated enzymes. They are considered promising templates for the engineering of designed bionanoreactors for biotechnology. In particular, encapsulation of oxidoreductive reactions requiring electron transfer between the lumen of the BMC and the cytosol relies on the ability to conduct electrons across the shell. We determined the crystal structure of a component protein of a synthetic BMC shell, which informed the rational design of a [4Fe-4S] cluster-binding site in its pore. We also solved the structure of the [4Fe-4S] cluster-bound, engineered protein to 1.8 Å resolution, providing the first structure of a BMC shell protein containing a metal center. The [4Fe-4S] cluster was characterized by optical and EPR spectroscopies; it has a reduction potential of -370 mV vs the standard hydrogen electrode (SHE) and is stable through redox cycling. This remarkable stability may be attributable to the hydrogen-bonding network provided by the main chain of the protein scaffold. The properties of the [4Fe-4S] cluster resemble those in low-potential bacterial ferredoxins, while its ligation to three cysteine residues is reminiscent of enzymes such as aconitase and radical S-adenosymethionine (SAM) enzymes. This engineered shell protein provides the foundation for conferring electron-transfer functionality to BMC shells.
细菌微室（BMC）是由选择性渗透的蛋白质外壳和包裹的酶组成的自组装细胞器。它们被认为是生物技术中设计仿生纳米反应器的有前途的模板。特别是，需要在 BMC 的内腔和细胞质之间进行电子转移的氧化还原反应的封装依赖于能够在壳层中传导电子的能力。我们确定了合成 BMC 壳的一种组成蛋白的晶体结构，这为其孔中的 [4Fe-4S] 簇结合位点的合理设计提供了信息。我们还解析了 [4Fe-4S] 簇结合的工程蛋白的结构，分辨率为 1.8 Å，提供了第一个含有金属中心的 BMC 壳蛋白的结构。[4Fe-4S] 簇通过光学和 EPR 光谱学进行了表征；它的还原电位为-370 mV 相对于标准氢电极（SHE），并且通过氧化还原循环稳定。这种显著的稳定性可能归因于蛋白质支架的主链提供的氢键网络。[4Fe-4S] 簇的性质类似于低电位细菌铁氧还蛋白的性质，而其与三个半胱氨酸残基的连接类似于 aconitase 和自由基 S-腺苷甲硫氨酸（SAM）酶等酶。这种工程化的壳蛋白为赋予 BMC 壳电子转移功能提供了基础。
