Eur. Phys. J. E 3, 315-321
Force probing of protein crystals: An atomic force microscopy study
V. Mollica1 - A. Relini1 - R. Rolandi1 - M. Bolognesi12 - A. Gliozzi1
1Department of Physics, University of Genoa, and INFM, Via
Dodecaneso 33, I-16146 Genoa, Italy
2 Advanced Biotechnology
Center, Largo R. Benzi 10, I-16132, Genoa, Italy
relini@fisica.unige.it
Received 10 February 2000 and Received in final form 4 May 2000
Abstract
The atomic force microscope (AFM) was used for measuring
force-distance curves on horse spleen ferritin crystals in liquid
environment. In the region of the approach curve which corresponds
to tip-surface contact, discrete jumps were recorded, as predicted
by molecular dynamics simulations in the case of low tip-sample
interaction. The observed jumps can be related to the removal of
individual molecules from the surface by the AFM tip. A simple
steric model, which takes into account tip and ferritin molecule
size, can explain the displacements
observed with excellent agreement.
The elemental force jump resulting from the approach
curves is a direct measure of the force required to remove a single
molecule from the crystal face. We discuss the conditions under
which the cantilever potential energy difference along the
elemental force step provides the energy of extraction of a single
molecule. The estimate of the intermolecular binding energy turns
out to be in good agreement with the value calculated independently
from the surface free energy of ferritin crystals.
PACS
87.14.Ee Proteins - 87.64.Dz Scanning tunneling and atomic
force microscopy
Copyright EDP Sciences, Società Italiana di Fisica, Springer-Verlag
