Why “Displacement” Misleads You: Allosteric Binding Demystified

Terry's Desk
Aug 26
3 min read

Kenakin’s latest lecture delivers a wake-up call for pharmacologists interpreting allosteric binding data. If you’re applying orthosteric logic to modulator-driven systems, you’re likely misreading your assays—and potentially misclassifying your leads.

This lesson helps you reframe how you interpret allosteric interactions—not as simple ligand displacement, but as transformations in receptor identity. You’ll learn how to recognize these shifts using vivid analogies (like Bruce Wayne vs. Batman) and master the Hall model to decode the thermodynamics behind complex binding behavior.

If your project involves GPCRs, functional selectivity, or non-traditional ligands, this session is essential.

In This Session, You’ll Gain:

✅ A clear explanation of why allosteric modulators don’t displace ligands—they change the protein species itself

✅ Real-world case studies showing binding-function dissociation and residual signal effects

✅ Tools to model binding with cooperativity factors (α, β, γ, σ) using the Hall allosteric cube

The Allosteric Shift: When Receptors Become Something New

In orthosteric pharmacology, a ligand is either on or off the receptor. More concentration = more competition = displacement. But in allosteric systems, adding a modulator doesn’t push another molecule off—it transforms the receptor into a different version of itself.

This isn’t just semantic. It redefines how we interpret radioligand curves, shifts in signal, and the meaning of “inhibition.” You’re no longer tracking the same protein species—and that changes everything.

Kenakin shows how even small cooperativity values (like α = 0.1) cap the shift in signal. No matter how much non-radioactive ligand you add, the binding curve levels off—because the receptor’s affinity state is redefined.

Binding vs. Function: Two Different Worlds

One of the most common—and dangerous—mistakes in allosteric pharmacology is expecting binding and function to match. Kenakin lays out why this is flawed.

Binding assays report on one set of receptor states. Functional assays track another. When a PAM increases radioligand binding but suppresses functional response, it’s not broken pharmacology—it’s biology working as designed.

This lesson shows how to read these patterns correctly—and how to avoid false conclusions in your lead prioritization.

Thermodynamics > Intuition: Why the Hall Cube Matters

To untangle complex binding behaviors, you need a model grounded in thermodynamics. Kenakin introduces the Hall model: a cube mapping allosteric and orthosteric interactions, layered with G protein binding.

Each face of the cube is governed by a cooperativity constant:

α: Modulator’s effect on radioligand binding
σ: Modulator’s effect on G protein coupling (efficacy)
γ: G protein’s effect on radioligand binding (efficacy of A)
β: Dual cooperativity—how ternary complexes influence each other

This framework explains partial signals, paradoxical responses, and the persistence of radiolabel even in “displaced” systems.

The G Protein Bottleneck: Why Stoichiometry Matters

In a standout case study, Kenakin shows how G protein availability determines whether you see “displacement” at all. A strong agonist, fails to reduce binding of a labeled NAM—not because of irreversibility, but because there isn’t enough G protein in the system to form the species that would lower the signal.

Switch cell lines. Add G protein. Suddenly, the agonist works.

The takeaway: what looks like pharmacology failure may be a systems problem. This insight could prevent wasted effort and reveal the true nature of your compound.

Allosteric Binding Is a Different Game. Learn the Rules.

If you’re still using orthosteric assumptions to interpret allosteric binding data, you're likely missing critical insights—or mislabeling your drug’s profile. This lecture gives you the language, models, and mindset to interpret these systems correctly and act with confidence in the lab.

Kenakin doesn’t just challenge assumptions. He gives you the tools to replace them.

Unlock “Allosteric Binding” Now

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