Molecular regulation and biosensing · BEGINNER LESSON
Sequestration
Sequestration is a mechanism in which one molecule binds a target tightly without producing a signal, lowering the free target until the binder is saturated. In biology and assays, this can make responses steeper, so small changes in target concentration cause larger changes in measured output.
What sequestration is and what it changes
In this lesson, sequestration means a binding process that changes how much free target is available to another molecule or pathway. The main thing being measured is target concentration, but the observable output is usually a signal from a second binding partner or a biological response. A depletant is a high-affinity molecule that binds the target without making a signal; a receptor or probe is a second molecule that does make a signal when it binds the target. This arrangement can make the output respond more sharply to small changes in target concentration. [0,2]
[1] The sequestration mechanism as a generalizable ... [3] High-Precision, In Vitro Validation of the Sequestration Mechanism for Generating Ultrasensitive Dose-Response Curves in Regulatory Networks
How the mechanism works
The depletant acts like a sink. At low target levels, most target is bound by the depletant, so little free target is available to the signaling receptor. Once total target exceeds the sink capacity, the depletant becomes saturated and the free target rises quickly. That extra free target then binds the lower-affinity receptor, producing a rapid increase in signal. In effect, sequestration turns a smooth binding curve into a steeper threshold-like response. [0,2]
[1] The sequestration mechanism as a generalizable ... [3] High-Precision, In Vitro Validation of the Sequestration Mechanism for Generating Ultrasensitive Dose-Response Curves in Regulatory Networks
Why scientists use it
In biosensors and bioassays, sequestration can improve the ability to measure small relative changes in target concentration by narrowing the dynamic range, meaning the span of concentrations over which the output changes usefully. The sources describe this as improving steepness and relative precision. A related cellular example is origin sequestration in Escherichia coli, where SeqA binds hemimethylated replication origins and temporarily inactivates them after DNA replication begins. That example shows sequestration can also regulate timing in cells, not only sensors. [0,1,2]
[1] The sequestration mechanism as a generalizable ... [2] ERIssue6.book(kvd116.fm) [3] High-Precision, In Vitro Validation of the Sequestration Mechanism for Generating Ultrasensitive Dose-Response Curves in Regulatory Networks
Limits and tradeoffs
Sequestration is not free of drawbacks. Making the response steeper usually shifts detection to higher target concentrations, which can worsen the limit of detection at the low end. The effect also depends on the concentration and affinity of the depletant relative to the receptor, so the behavior must be tuned carefully. In E. coli, sequestration is only one of several mechanisms that prevent repeated DNA replication; other controls also contribute. [0,1,2]
[1] The sequestration mechanism as a generalizable ... [2] ERIssue6.book(kvd116.fm) [3] High-Precision, In Vitro Validation of the Sequestration Mechanism for Generating Ultrasensitive Dose-Response Curves in Regulatory Networks
SEE THE IDEA
How sequestration changes a binding response
The molecule whose concentration is being measured or controlled.
High-affinity, non-signaling binder that lowers free target.
State where the depletant can no longer hold all added target.
Lower-affinity binder that generates the readout.
Target is first captured by the depletant; after saturation, extra target reaches the signal receptor and the output rises sharply.
A depletant hides target until its capacity is filled, then a signaling receptor converts the rising free target into a steeper measurable response.
TRY IT YOURSELF
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.