Structure and stability of pertussis toxin studied by in situ atomic force microscopy

Pertussis toxin, both complete and the B-oligomer, were imaged by atomic force microscopy (AFM), using specimens prepared by simple surface adsorption on mica without further manipulation. The spatial arrangement of the subunits of the B-oligomer was clearly resolved, representing the first protein quaternary structure obtained by AFM in situ. The results suggest that the B-oligomer is a flat pentamer with the two large subunits located next to each other, and the catalytic A-subunit situated at the center above. We found that the B-pentamer was structurally stable for temperatures up to 60 degrees C and within the pH range of 4.5-9.5. It is also demonstrated that the AFM was capable of resolving features down to 0.5 nm on the B-oligomers, indicating its great potential for structural determination.