Conformational rearrangements of an archaeal chaperonin upon ATPase cycling.
Chaperonins are double-ring protein assemblies with a central cavity that provides a sequestered environment for in vivo protein folding. Their reaction cycle is thought to consist of a nucleotide-regulated alternation between an open substrate-acceptor state and a closed folding-active state. The cavity of ATP-charged group I chaperonins, typified by Escherichia coli GroEL [1], is sealed off by a co-chaperonin, whereas group II chaperonins--the archaeal thermosome and eukaryotic TRiC/CCT [2]--possess a built-in lid [3-5]. The mechanism of the lid's rearrangements requires clarification, as even in the absence of nucleotides, thermosomes of Thermoplama acidophilum appear open in vitrified ice [6] and closed in crystals [4]. Here we analyze the conformation of the thermosome at each step of the ATPase cycle by small-angle neutron scattering. The apo-chaperonin is open in solution, and ATP binding induces its further expansion. Closure seems to occur during ATP hydrolysis and before phosphate release, and represents the rate-limiting step of the cycle. The same closure can be triggered by the crystallization buffer. Thus, the allosteric regulation of group II chaperonins appears different from that of their group I counterparts.
Gutsche
I
I
Max-Planck-Institute for Biochemistry, Martinsried bei München, D-82152, Germany. gutsche@biochem.mpg.de
Holzinger
J
J
Rössle
M
M
Heumann
H
H
Baumeister
W
W
May
R P
RP
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D019843:Archaeal Proteins / Q000737:chemistry*; D018833:Chaperonins / Q000737:chemistry*; D008962:Models, Theoretical; D009502:Neutrons; D011487:Protein Conformation; D012542:Scattering, Radiation; D012996:Solutions; D013822:Thermoplasma; D056405:Thermosomes
D019843:Archaeal Proteins; D012996:Solutions; D000251:Adenosine Triphosphatases; D018833:Chaperonins; D056405:Thermosomes