TY - JOUR
T1 - At sixes and sevens
T2 - Characterization of the symmetry mismatch of the ClpAP chaperone-assisted protease
AU - Beuron, Fabienne
AU - Maurizi, Michael R.
AU - Belnap, David M.
AU - Kocsis, Eva
AU - Booy, Frank P.
AU - Kessel, Martin
AU - Steven, Alasdair C.
PY - 1998/11
Y1 - 1998/11
N2 - ClpAP, a typical energy-dependent protease, consists of a proteolytic component (ClpP) and a chaperone-like ATPase (ClpA). ClpP is composed of two apposed heptameric rings, whereas in the presence of ATP or ATPγS, ClpA is a single hexameric ring. Formation of ClpAP complexes involves a symmetry mismatch as sixfold ClpA stacks axially on one or both faces of sevenfold ClpP. We have analyzed these structures by cryo-electron microscopy. Our three-dimensional reconstruction of ClpA at 29-Å resolution shows the monomer to be composed of two domains of similar size that, in the hexamer, form two tiers enclosing a large cavity. Cylindrical reconstruction of ClpAP reveals three compartments: the digestion chamber inside ClpP; a compartment between ClpP and ClpA; and the cavity inside ClpA. They are connected axially via narrow apertures, implying that substrate proteins should be unfolded to allow translocation into the digestion chamber. The cavity inside ClpA is structurally comparable to the 'Anfinsen cage' of other chaperones and may play a role in the unfolding of substrates. A geometrical description of the symmetry mismatch was obtained by using our model of ClpA and the crystal structure of ClpP (Wang et al., 1997, Cell 91, 447-456) to identify the particular side views presented by both molecules in individual complexes. The interaction is characterized by a key pair of subunits, one of each protein. A small turn (8.6°= 2π/42; equivalent to a 4-Å shift) would transfer the key interaction to another pair of subunits. We propose that nucleotide hydrolysis results in rotation, facilitating the processive digestion of substrate proteins.
AB - ClpAP, a typical energy-dependent protease, consists of a proteolytic component (ClpP) and a chaperone-like ATPase (ClpA). ClpP is composed of two apposed heptameric rings, whereas in the presence of ATP or ATPγS, ClpA is a single hexameric ring. Formation of ClpAP complexes involves a symmetry mismatch as sixfold ClpA stacks axially on one or both faces of sevenfold ClpP. We have analyzed these structures by cryo-electron microscopy. Our three-dimensional reconstruction of ClpA at 29-Å resolution shows the monomer to be composed of two domains of similar size that, in the hexamer, form two tiers enclosing a large cavity. Cylindrical reconstruction of ClpAP reveals three compartments: the digestion chamber inside ClpP; a compartment between ClpP and ClpA; and the cavity inside ClpA. They are connected axially via narrow apertures, implying that substrate proteins should be unfolded to allow translocation into the digestion chamber. The cavity inside ClpA is structurally comparable to the 'Anfinsen cage' of other chaperones and may play a role in the unfolding of substrates. A geometrical description of the symmetry mismatch was obtained by using our model of ClpA and the crystal structure of ClpP (Wang et al., 1997, Cell 91, 447-456) to identify the particular side views presented by both molecules in individual complexes. The interaction is characterized by a key pair of subunits, one of each protein. A small turn (8.6°= 2π/42; equivalent to a 4-Å shift) would transfer the key interaction to another pair of subunits. We propose that nucleotide hydrolysis results in rotation, facilitating the processive digestion of substrate proteins.
KW - Clp protease
KW - Electron microscopy
KW - Energy-dependent proteolysis
KW - Symmetry
KW - Three-dimensional image reconstruction.
UR - http://www.scopus.com/inward/record.url?scp=0032215219&partnerID=8YFLogxK
U2 - 10.1006/jsbi.1998.4039
DO - 10.1006/jsbi.1998.4039
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C2 - 9878579
AN - SCOPUS:0032215219
SN - 1047-8477
VL - 123
SP - 248
EP - 259
JO - Journal of Structural Biology
JF - Journal of Structural Biology
IS - 3
ER -