STRATEGIES IN THE CRYSTALLIZATION OF GLYCOPROTEINS AND PROTEIN COMPLEXES

Modern biochemical and molecular biological techniques have provided new opportunities to investigate the structure of more complex biomolecules and have opened new paths for the crystallization of complexes. Desialation, deglycosylation and modification of glycoproteins are techniques being investigated as a means of making glycosylated proteins more amenable for crystallization. A simple solubility screen based on a limited set of precipitants has been extensively used in the comparison of various protein preparations and in the crystallization of macromolecular complexes. Antibodies, or their Fabs or Fab' fragments, can also be utilized in the crystallization of glycoproteins or other proteins which have proved difficult to crystallize by themselves. Fab complexes can provide different surfaces for lattices to form and may increase the likelihood of crystallizing a given protein. This method can be extended by the addition of an epitope tag, such as a short peptide sequence, to a protein by genetic engineering methods. The same panel of anti-peptide antibodies can then be utilized in both the purification and crystallization of different expressed proteins, making this a potential general method for protein crystallization.