Heldt Dana, Frank Stefanie, Seyedarabi Arefeh, Ladikis Dimitrios, Parsons Joshua B, Warren Martin J, Pickersgill Richard W
Centre for Molecular Processing, School of Biosciences, University of Kent, Giles Lane, Canterbury, Kent, UK.
Biochem J. 2009 Sep 25;423(2):199-207. doi: 10.1042/BJ20090780.
It has been suggested that ethanol metabolism in the strict anaerobe Clostridium kluyveri occurs within a metabolosome, a subcellular proteinaceous bacterial microcompartment. Two bacterial microcompartment shell proteins [EtuA (ethanol utilization shell protein A) and EtuB] are found encoded on the genome clustered with the genes for ethanol utilization. The function of the bacterial microcompartment is to facilitate fermentation by sequestering the enzymes, substrates and intermediates. Recent structural studies of bacterial microcompartment proteins have revealed both hexamers and pentamers that assemble to generate the pseudo-icosahedral bacterial microcompartment shell. Some of these shell proteins have pores on their symmetry axes. Here we report the structure of the trimeric bacterial microcompartment protein EtuB, which has a tandem structural repeat within the subunit and pseudo-hexagonal symmetry. The pores in the EtuB trimer are within the subunits rather than between symmetry related subunits. We suggest that the evolutionary advantage of this is that it releases the pore from the rotational symmetry constraint allowing more precise control of the fluxes of asymmetric molecules, such as ethanol, across the pore. We also model EtuA and demonstrate that the two proteins have the potential to interact to generate the casing for a metabolosome.
有人提出，严格厌氧菌克氏梭菌中的乙醇代谢发生在代谢体中，代谢体是一种亚细胞蛋白质细菌微区室。在基因组上发现两种细菌微区室外壳蛋白[EtuA（乙醇利用外壳蛋白A）和EtuB]与乙醇利用基因聚集在一起。细菌微区室的功能是通过隔离酶、底物和中间体来促进发酵。最近对细菌微区室蛋白的结构研究揭示了组装形成假二十面体细菌微区室外壳的六聚体和五聚体。其中一些外壳蛋白在其对称轴上有孔。在这里，我们报告三聚体细菌微区室蛋白EtuB的结构，其亚基内有串联结构重复且具有假六边形对称性。EtuB三聚体中的孔在亚基内而非对称相关亚基之间。我们认为这样做的进化优势在于它使孔摆脱了旋转对称性的限制，从而能够更精确地控制不对称分子（如乙醇）通过孔的通量。我们还对EtuA进行了建模，并证明这两种蛋白质有可能相互作用以生成代谢体的外壳。
