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Six‐fold rotational symmetry of ClpQ, the E. coli homolog of the 20S proteasome, and its ATP‐dependent activator, ClpY
Author(s) -
Kessel Martin,
Wu Whi-fin,
Gottesman Susan,
Kocsis Eva,
Steven Alasdair C.,
Maurizi Michael R.
Publication year - 1996
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(96)01261-6
Subject(s) - protein subunit , dodecameric protein , chaperone (clinical) , chemistry , protease , crystallography , operon , size exclusion chromatography , biophysics , biochemistry , biology , enzyme , escherichia coli , dna , gene , medicine , pathology
ClpQ (HsIV) is a homolog of the β‐subunits of the 20S proteasome. In E. coli , it is expressed from an operon that also encodes ClpY (HsIU), an ATPase homologous to the protease chaperone, ClpX. ClpQ (subunit M r 19 000) and ClpY (subunit M r 49 000) were purified separately as oligomeric proteins with molecular weights of ∼220 000 and ∼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.