Surface
Reconstruction on Protein Crystals
Surface Reconstruction is the technical
term for the difference between the packing arrangement of the surfaces
of crystals from that in the crystal interior. This is a well known
phenomenon in inorganic crystals. It is believed to occur because
the surface molecules have incomplete bonds and because they are in contact
with the solvent, unlike molecules in the crystal interior. It was
not known if this phenomena would occur in protein crystals, as in these
crystals the molecules in the interior are also in contact with the solvent
phase. While trying to determine the
molecular packing arrangements on tetragonal lysozyme crystal faces with
high resolution AFM, we observed the surface reconstruction phenomenon
for the first time on a protein crystal.
 |
Figure 1:
Comparison between
an experimental AFM image and a theoretical one for the (110) face of tetragonal
lysozyme crystals. The theoretical image was constructed for a packing
arrangement with complete 43 helices. This packing corresponds
to that of the crystal interior obtained from X-ray crystallography. This
theoretical image is shown here embedded in the experimental
AFM image (see also the
section on surface packing). The correlation between the two
images is 62%. The whole image has been slightly tilted to show 3D features. |
 |
Figure 2:
Same image as
figure 1, but the theoretical image was constructed by modifying the packing
slightly. The molecules were moved closer to the 43 axis
by 7Å from the crystallographic arrangement of the interior. The
correlation between the new theoretical image and the experimental one
is now 93%. |
The results shown in the above figures were
duplicated by other collected high resolution AFM images on the (110) faces
of tetragonal lysozyme. They all showed that on the surface the molecules
were packed closer to the 43 axes by ~7A than the crystallographic
arrangement. For more details see H.
Li, M.A. Perozzo, J.H. Konnert, A. Nadarajah & M.L. Pusey, Acta
Crystallographica, D55, 1023-1035 (1999).
Return to the homepages of:
