  As proteins typically have charges of around 10, they will interact strongly
with charged surfaces. We calculate the electrostatic contribution to the
interaction of crystals of protein with charged surfaces. The surfaces repel
like-charged crystals and attract oppositely-charged crystals, with free
energies which can be easily several kT per protein molecule brought into
contact with the surface. This means that oppositely charged surfaces can act
as a nucleant, they can induce nucleation of a protein crystal by lowering the
free energy barrier to heterogeneous nucleation of the crystal from a dilute
solution.

Soft Condensed Matter;Biomolecules