Crystal structure of the beta-apical domain of the thermosome reveals structural plasticity in the protrusion region.
The crystal structure of the beta-apical domain of the thermosome, an archaeal group II chaperonin from Thermoplasma acidophilum, has been determined at 2.8 A resolution. The structure shows an invariant globular core from which a 25 A long protrusion emanates, composed of an elongated alpha-helix (H10) and a long extended stretch consisting of residues GluB245-ThrB253. A comparison with previous apical domain structures reveals a large segmental displacement of the protruding part of helix H10 via the hinge GluB276-ValB278. The region comprising residues GluB245-ThrB253 adopts an extended beta-like conformation rather than the alpha-helix seen in the alpha-apical domain. Consequently, it appears that the protrusions of the apical domains from group II chaperonins might assume a variety of context-dependent conformations during an open, substrate-accepting state of the chaperonin. Sequence variations in the protrusion regions that are found in the eukaryotic TRiC/CCT subunits may provide different structural propensities and hence serve different roles in substrate recognition.
Max-Planck-Institute for Biochemistry, Am Klopferspitz 18a, Martinsried bei München, D-82152, Germany.
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Baumeister
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Essen
D019843:Archaeal Proteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D018833:Chaperonins / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D018583:Pliability; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity; D013822:Thermoplasma / Q000737:chemistry*; D056405:Thermosomes
D019843:Archaeal Proteins; D018833:Chaperonins; D056405:Thermosomes