High resolution surface structure of E-coli GroES oligomer by atomic force microscopy

Using atomic force microscopy (AFM) in aqueous solution, we show that the surface structure of the oligomeric GroES can be obtained up to 10 Angstrom resolution, The seven subunits of the heptamer were web resolved without image averaging. The overall dimension of the GroES heptamer was 8.4+/-0.4 nm in diameter and 3.0+/-0.3 nm high, However, the AFM images further suggest that there is a central protrusion of 0.8+/-0.2 nm high and 4.5+/-0.4 nm in diameter on one side of GroES which displays a profound seven-fold symmetry, It was found that GroEL could not bind to the adsorbed GroES in the presence of AMP-PNP and Mg2+, suggesting that the side of GroES with the central protrusion faces away from the GroEL lumen, because only one side of GroES was observed under these conditions. Based on the results from both electron and atomic force microscopy, a surface model for the GroES is proposed.