Crystal Structure of Escherichia coli GroEL in Substrate and ADP Unloaded State

E. coli GroEL is a member of ATP-dependent chaperonin family and is involved in proper folding of cytosolic bacterial proteins. The E. coli GroEL contains 14 identical subunits of ~58.3 kD and arranged as two stalked rings. In current study, we have determined the X-ray structure of E. coli GroEL at 3.2-A resolution. The GroEL protein was coexpressed during recombinant M. tuberculosis DprE1 protein expression in E. coli and was co-purified with DprE1. The GroEL-DprE1 complex was crystallized and x-ray structure analysis yielded electron density for only GroEL protein only and no density for DrpE1 protein. Comparison of our GroEL structure with previous wild type GroEL (PDB-1XCK), DM-GroEL-(ATP)14 (PDB-1KP8) and GroEL- GroES-(ADP)7 (PDB-1PF9) structures have yielded the differences in (i) interactions between heptameric rings involved in allosteric signaling (ii) interactions within heptameric ring, (iii) H and I helices of apical domain involved in substrate binding and (iv) residues involved in signaling route. These results indicate that our GroEL structure may be in different state, which occurred during protein folding cycle after unloading the substrate and ADP.