Stabilization of surface-immobilized enzymes using grafted polymers

We introduce a two-dimensional lattice model of immobilization and stabilization of proteinlike polymers using grafted polymers. The protein is designed to have a specific bulk conformation reproducing a catalytic cleft of natural enzymes. Our model predicts a first order denaturing adsorption transition of free proteins. On the other hand, for an immobilized protein we observe a more gradual disappearance of the hydrophobic centers accompanied by adsorption. We show that, using hydrophilic grafted polymers of proper length and grafting density, the conformation as well as the hydrophobic centers of the protein can be restored.

Figure 1

Density profiles of a dimeric protein as a function of $x\text{−}z$ location in simulation box (length in dimensionless units): (a) bulk and (b) adsorbed conformation. ${\chi }_{23}=\pm 0.5$, ${\chi }_{2s}=\pm 2.0\left(s=\text{surface}\right)$.

Figure 2

Density profiles of an immobilized protein as a function of $x\text{−}z$ location in simulation box (length in dimensionless units). $z_{\text{fix}}=12$, (a) adsorption begins; (b) 11; and (c) 10, peaks designating active sites have essentially disappeared.

Figure 3

Density profiles of the protein immobilized at $z_{\text{fix}}=9$, stabilized by hydrophilic grafted polymers as a function of $x\text{−}z$ location in simulation box (length in dimensionless units). (a) Noninteracting polymers $\left({\chi }_{12}=0\right);$ (b) hydrophilic polymers $\left({\chi }_{12}=\pm 0.2\right)$.These results are for $N_1=20$ and $\sigma =0.1$.

Figure 4

Excess free energy as a function of dimensionless distance of the center of the protein from the surface for a free protein (triangles), an immobilized protein (squares), and an immobilized protein stabilized by hydrophilic grafted polymers (circles) for $N=20$, $\sigma =0.1$, and ${\chi }_{12}=\pm 0.2$.