ATP-induced structural change of the thermosome is temperature-dependent.
Protein folding by chaperonins is powered by ATP binding and hydrolysis. ATPase activity drives the folding machine through a series of conformational rearrangements, extensively described for the group I chaperonin GroEL from Escherichia coli but still poorly understood for the group II chaperonins. The latter--archaeal thermosome and eukaryotic TRiC/CCT--function independently of a GroES-like cochaperonin and are proposed to rely on protrusions of their own apical domains for opening and closure in an ATP-controlled fashion. Here we use small-angle neutron scattering to analyze structural changes of the recombinant alpha-only and the native alphabeta-thermosome from Thermoplasma acidophilum upon their ATPase cycling in solution. We show that specific high-salt conditions, but not the presence of MgATP alone, induce formation of higher order thermosome aggregates. The mechanism of the open-closed transition of the thermosome is strongly temperature-dependent. ATP binding to the chaperonin appears to be a two-step process: at lower temperatures an open state of the ATP-thermosome is predominant, whereas heating to physiological temperatures induces its switching to a closed state. Our data reveal an analogy between the ATPase cycles of the two groups of chaperonins and enable us to put forward a model of thermosome action.
Gutsche
I
I
Max-Planck-Institute for Biochemistry, Am Klopferspitz 18a, Martinsried bei München, D-82152, Germany.
Holzinger
J
J
Rauh
N
N
Baumeister
W
W
May
R P
RP
D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology*; D019843:Archaeal Proteins / Q000737:chemistry / Q000378:metabolism; D002021:Buffers; D018833:Chaperonins / Q000737:chemistry* / Q000378:metabolism; D019281:Dimerization; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology; D008956:Models, Chemical; D009502:Neutrons; D011485:Protein Binding / Q000187:drug effects; D011487:Protein Conformation / Q000187:drug effects; D012542:Scattering, Radiation; D013696:Temperature; D056405:Thermosomes
D019843:Archaeal Proteins; D002021:Buffers; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D018833:Chaperonins; D056405:Thermosomes; D008274:Magnesium