RESUMO
The production of recombinant proteins in Escherichia coli cells is often hampered by aggregation of newly synthesized proteins and formation of inclusion bodies. Here we propose the use of transverse urea gradient electrophoresis (TUGE) in testing the capability of folding of a recombinant protein from inclusion bodies dissolved in urea. A plasmid encoding the amino acid sequence 55-224 of TcpA pilin (C-terminal globular domain: TcpA-C) from Vibrio cholerae El Tor enlarged by a His-tag on its N-terminus was expressed in E. coli cells. The major fraction (about 90%) of the target polypeptide was detected in cell debris. The polypeptide was isolated from the soluble fraction and recovered from inclusion bodies after their urea treatment. Some structural properties of the polypeptide from each sample proved identical. The refolding protocol was developed on the basis of TUGE data and successfully used for the protein large-scale recovery from inclusion bodies. Spectral, hydrodynamic, and thermodynamic characteristics of the recombinant TcpA recovered from inclusion bodies indicate the presence of a globular conformation with a pronounced secondary structure and a rigid tertiary structure, which is promising for the design of immunodiagnostics preparations aimed to assess the pilin level in different strains of V. cholerae and to develop cholera vaccines.
RESUMO
Chaperonin GroEL is a complex oligomeric heat shock protein (Hsp60) assisting the correct folding and assembly of other proteins in the cell. An intriguing question is how GroEL folds itself. According to the literature, GroEL reassembly is dependent on chaperonin ligands and solvent composition. Here we demonstrate dependence of GroEL reassembly efficiency on concentrations of the essential factors (Mg2+, ADP, ATP, GroES, ammonium sulfate, NaCl and glycerol). Besides, kinetics of GroEL oligomerization in various conditions was monitored by the light scattering technique and proved to be two-exponential, which suggested accumulation of a certain oligomeric intermediate. This intermediate was resolved as a heptamer by nondenaturing blue electrophoresis of GroEL monomers during their assembly in the presence of both Mg-ATP and co-chaperonin GroES. Presumably, this intermediate heptamer plays a key role in formation of the GroEL tetradecameric particle. The role of co-chaperonin GroES (Hsp10) in GroEL assembly is also discussed.
