Equilibrium and dynamic design principles for binding molecules engineered for reagentless biosensors
Section snippets
Model formulation
The system consists of three state variables: the concentrations of ligand (L), unbound sensor (SF) and bound sensor (SB). By virtue of mass balance, the sum of the concentration of unbound and bound sensor is always equal to the total sensor concentration constant (STot). A linear correlation between the bound sensor and the output signal intensity is assumed. The two rate constants governing this process are the association (kon) and the dissociation (koff) rate constant.
The mathematical
Dynamic consideration reveals the crucial importance of kinetic rates optimization
Intuitively, a sensor that has a very high affinity for its ligand might be expected to perform as a weak dynamic sensor since the characteristic time for complex dissociation would likely be much greater than the period of the signal. Relevant input signal conditions depend greatly on the system under study. In Fig. 1 we show approximate concentrations and time scales for concentration variation for various classes of biological events. Many physiological processes result in great variation of
Discussion
We have shown that there exists an optimal combination of the design parameters kon and koff for a reagentless biosensor and that these vary depending on the nature of the signal. What our results indicate is that the careful determination of binding kinetics is crucial for successful application of biosensors. As a general rule, the KD of the interaction must match that of the expected mean ligand concentration to ensure greatest sensitivity. Biosensors with a KD lower that the mean ligand
Acknowledgments
The authors thank Dr. Alan Wells and Dr. Neda Bagheri for helpful discussions. This work was supported by the Integrative Cancer Biology Program (ICBP 1 U54 CA112967) and by NIH R01 EB 010246.
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