Folding of thermolysin fragments. Hydrodynamic properties of isolated domains and subdomains.
Sedimentation analysis in the analytical ultracentrifuge has been used to characterize the size and shape of thermolysin and a number of its fragments obtained by chemical or enzymatic cleavage of the protein. Four fragments (121-316, 206-316, 225/226-316 and 255-316) originate from the C-terminal domain, and two (1-155 and 1-205) from the N-terminal domain of the intact molecule. In aqueous solution at neutral pH the hydrodynamic properties of the C-terminal fragments, except 255-316, are consistent with compact homogeneous monomers. Fragment 255-316 is a monomeric species below 0.08 mg/ml concentration and forms a dimer above this concentration. Dimerization does not lead to changes in fragment conformation, as determined by far-ultraviolet circular dichroic measurements, but to an increase of 5.6 degrees C (to 68.2 degrees C at 1.0 mg/ml) in the temperature for thermal unfolding and a corresponding increase of 4.6 kJ/mol in the free energy of unfolding. Fragments derived from the N-terminal domain show a strong tendency to form high-molecular-mass aggregates. Previous experiments utilizing circular dichroic measurements and antibody binding data suggested that the C-terminal fragments listed above are able to refold in aqueous solution at neutral pH into a stable conformation of native-like characteristics [Dalzoppo, D., Vita, C. & Fontana, A. (1985) J. Mol. Biol. 182, 331-340] (and references cited therein). Present data establish that all these C-terminal fragments are globular monomeric species in solution (at concentrations approximately 0.1 mg/ml) and thus represent 'isolated' domains (or subdomains) with intrinsic conformational stability typical of small globular proteins.
Department of Organic Chemistry, University of Padua, Italy.
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Vita
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Fontana
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Jaenicke
D001407:Bacillus / Q000201:enzymology; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010446:Peptide Fragments; D011487:Protein Conformation; D011489:Protein Denaturation; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics; D013820:Thermolysin; D014461:Ultracentrifugation / Q000379:methods
D010446:Peptide Fragments; D013820:Thermolysin