The molecular chaperonin TF55 from the Thermophilic archaeon Sulfolobus solfataricus. A biochemical and structural characterization.
The purification and characterization of a new type of thermostable chaperonin from the archaebacterium Sulfolobus solfataricus is described. The chaperonin forms a hetero-oligomeric complex of two different, but closely related, subunits, which we have assigned TF55-alpha and TF55-beta. Their N-terminal sequences and amino acid residue compositions are reported. Two-dimensional projections of the chaperonin have been reconstructed from electron microscopy images, showing a 9-fold symmetrical complex, about 17.5 nm in height and 16 nm in diameter, with a central cavity of 4.5 nm. The complex is resistant to denaturing agents at room temperature and only pH values lower than 2 lead to dissociation. The separated subunits do not reassemble spontaneously but require Mg2+ and ATP for complex formation. Both subunits are necessary for formation of the TF55 oligomer. Significant structural changes have been observed after phosphorylation, thus providing evidence for a structural mobility during the chaperonin-assisted folding process of a protein. The phosphorylation reaction is modulated by potassium and magnesium ions. Magnesium seems to have an inhibitory effect, whereas potassium enhances this reaction.
Knapp
S
S
Karolinska Institutet, NOVUM, Center for Structural Biochemistry, Huddinge, Sweden.
Schmidt-Krey
I
I
Hebert
H
H
Bergman
T
T
Jörnvall
H
H
Ladenstein
R
R
D000595:Amino Acid Sequence; D019843:Archaeal Proteins; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D018832:Molecular Chaperones / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D010766:Phosphorylation; D016944:Sulfolobus / Q000378:metabolism*
D019843:Archaeal Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; C072010:TF55 protein, Sulfolobus shibatae