[Structural features of proteins by intermittent-contact atomic force microscopy]

Optimal conditions of protein scanning by atomic force microscopy were developed. Proteins of different molecular masses (950-11.5 kDa) and different three-dimensional organization were used to investigate the structural features of proteins. The most distinct images of proteins were obtained using a tip with the free amplitude in the range of 5-15 nm and with the set-point amplitude in the regime of repulsion from the sample. The method allowed one to clearly recognize the structural details of large molecules such as immunoglobulins IgM and IgG1 and Ricinus agglutinin. The revealing of the structural properties of proteins with molecular masses of 60 kDa and less was limited by the sharpness of probe tips used in the present study. It was shown that, by a quantitative analysis of the geometric parameters of molecules, it is possible to distinguish IgG1, Ricinus agglutinin, and ricin.