Gels Mimicking Antibodies in Their Selective Recognition of Proteins and Its Potential Use for Protein Crystallization - Molecules: Nucleation, Aggregation and Crystallization - page 25

monomers which give rise to very strong bonds should be replaced by
those interacting more weakly. To attain a strong overall binding the number
of bonds must, accordingly, be large. Examples of weak interactions are those
originating from hydrogen bonds, charge transfer, faint induced dipoles and
slightly non-polar groups. Acrylamide and N,N -methylenebisacrylamide

represent appropriate monomers. Gels synthesized from these monomers
are widely used in many standard methods for electrophoresis and chro-
matography. All accumulated experience shows that these gels are very
inert to biopolymers, including proteins.
A very close contact between a protein molecule and polymer chains
in the gel is, accordingly, a prerequisite for the generation of bonds. This
proximity is created when the monomers polymerize around the protein
molecule (and may increase the strength of each bond). If the discussed
hypothesis for selective recognition is correct, one should expect a protein
of a relatively small size (and therefore fewer adsorption sites) to interact
only weakly with gels of a composition similar to that employed in this
investigation. Therefore, we studied the behavior of insulin (molecular
weight: 5700 daltons) on a T6, C5 gel prepared in the presence of insulin.
The protein was much less adsorbed than were larger proteins, such as
growth hormone and transferrin, but the interaction was nevertheless
selective because the elution volume was 40% larger than that obtained on
a blank gel synthesized in the absence of insulin (not shown here).

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Some comments on the mechanism
of selective recognition

In the 1960s it was shown that proteins could be immobilized in a gel for
bio-affinity chromatography if they were included in the monomer solu-
tion (Bernfeld, Wan, 1963; Kennedy, Cabra, 1983). It was postulated that
the immobilization consisted of occlusion of the protein molecules in the
polymeric network. In view of the properties of the gels described herein,
it is likely that at least part of the immobilization originated from selec-
tive adsorption and not by entrapment caused by occlusion. It is known
that cross-linking of agarose gels with divinyl sulfone causes some