Kessel M, Wu W, Gottesman S, Kocsis E, Steven A C, Maurizi M R
Laboratory of Structural Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, Bethesda, MD 20892, USA.
FEBS Lett. 1996 Dec 2;398(2-3):274-8. doi: 10.1016/s0014-5793(96)01261-6.
ClpQ (HslV) is a homolog of the beta-subunits of the 20S proteasome. In E. coli, it is expressed from an operon that also encodes ClpY (HslU), an ATPase homologous to the protease chaperone, ClpX. ClpQ (subunit Mr 19,000) and ClpY (subunit Mr 49,000) were purified separately as oligomeric proteins with molecular weights of approximately 220,000 and approximately 350,000, respectively, estimated by gel filtration. Mixtures of ClpY and ClpQ displayed ATP-dependent proteolytic activity against casein, and a complex of the two proteins was isolated by gel filtration in the presence of ATP. Image processing of negatively stained electron micrographs revealed strong six-fold rotational symmetry for both ClpY and ClpQ, suggesting that the subunits of both proteins are arranged in hexagonal rings. The molecular weight of ClpQ combined with its symmetry is consistent with a double hexameric ring, whereas the data on ClpY suggest only one such ring. The symmetry mismatch previously observed between hexameric ClpA and heptameric ClpP in the related ClpAP protease is apparently not reproduced in the symmetry-matched ClpYQ system.
ClpQ（HslV）是20S蛋白酶体β亚基的同源物。在大肠杆菌中，它由一个操纵子表达，该操纵子还编码ClpY（HslU），一种与蛋白酶伴侣ClpX同源的ATP酶。通过凝胶过滤估计，ClpQ（亚基分子量为19,000）和ClpY（亚基分子量为49,000）分别作为分子量约为220,000和约350,000的寡聚蛋白被纯化。ClpY和ClpQ的混合物对酪蛋白显示出ATP依赖性蛋白水解活性，并且在ATP存在下通过凝胶过滤分离出这两种蛋白质的复合物。对负染电子显微镜照片进行图像处理显示，ClpY和ClpQ都具有强烈的六重旋转对称性，这表明这两种蛋白质的亚基都排列成六边形环。ClpQ的分子量与其对称性一致，表明它是一个双六聚体环，而关于ClpY的数据仅表明它是一个这样的环。之前在相关的ClpAP蛋白酶中观察到的六聚体ClpA和七聚体ClpP之间的对称性不匹配显然在对称匹配的ClpYQ系统中没有重现。
