Chemistry Reference
In-Depth Information
Chart 2.8 Structures of bolamphiphilic homopolymers.
2.3.2. Recognition of Protein Surfaces
Amphiphilic polymers form flexible assemblies; hence, they can change their confor-
mation upon binding to a surface. This interesting property coupled with the easy
modification of charge can be used for recognition of biomolecules like proteins,
without necessarily denaturing their structure. This noncovalent binding between
proteins and charged polymers could be useful in modulating protein-protein inter-
actions and protein-DNA interactions (Fischer et al. 2002, 2003; Hong et al. 2004).
We studied the interaction of anionic polymer micelles with positive patches of chy-
motrypsin (ChT; Sandanaraj et al. 2005). Amphiphilic polymer micelles are
40 nm
in size with negatively charged carboxylate groups on the surface. Because these
polymeric micelles expose a huge amount of negative charges on the surface, we
expected them to recognize the positive patch of proteins by electrostatic attraction.
Figure 2.8 is a schematic representation of the interaction of proteins with the
polymeric micelles.
Polymer-protein binding affinity was studied qualitatively through nondenaturing
gel electrophoresis, fluorescence spectroscopy, and enzymatic assay. The formation
of the polymer-protein complex and the electrostatic basis of the interaction were
confirmed by the inhibition of the enzymatic activity and the recovery of this activity
at high ionic strengths, respectively. The dissociation constant of polymer 11 with the
protein was determined to be 7
10
27
M with a polymer/ChT binding ratio of 1:10.
Perhaps the most interesting aspect of this study is the artificial selectivity that this
interaction brought to the enzyme toward its substrates. The modulation in activity
Figure 2.8
Interaction of anionic amphiphilic homopolymeric micelle with the positive patch
of protein.
