Anisotropic intersubunit and inter-ring interactions revealed in the native bullet-shaped chaperonin complex from...

The recent morphological studies on chaperonins have revealed that nearly equivalent amount of symmetric GroEL-(GroES)2 (football-shaped) and asymmetric GroEL-GroES (bullet-shaped) complexes coexist during the chaperonin reaction cycle, which prompted us to reexamine the equatorial split observed for chaperonin from Thermus thermophilus by implementing semi-empirical molecular orbital (MO) calculations, since it is now believed that the symmetric formation is a precursor to the equatorial split.

Semi-empirical MO calculations were employed to investigate the intersubunit interactions within the bullet-shaped T. thermophilus chaperonin capturing the substrate of folding intermediates. Interaction energies between each cis-GroEL subunit and closely related remaining subunits in cis-GroEL ring, or in trans-GroEL ring across the equatorial plane, and further, interaction energies between each GroES subunit and adjacent subunits in the same GroES ring and in cis-GroEL ring were simulated.

Anisotropic intensities and energy distribution of the subunits were revealed by the calculations, which are consistent with two conformations of the subunits forming cis-GroEL ring as revealed by X-ray crystal structure, and with an anisotropic critical binding site on cis-GroEL ring for chaperonin functioning.

This is the first application of semi-empirical MO calculations to the macromolecular complex of the native bullet-shaped chaperonin (GroEL-GroES-ADP homolog) from T. thermophilus.

The results also appear to support the occurrence of the equatorial split for T. thermophilus chaperonin observed via electron microscopy, but has not yet been fully observed for Escherichia coli GroEL-GroES system.