Thermal proteome profiling (TPP, also called CETSA at single-protein scale) heats intact cells or lysate to a series of temperatures, pellets the proteins that unfold and aggregate by centrifugation, and quantifies whatever stays in the soluble supernatant by mass spectrometry. In this simulator every one of the 30 copies in a population carries its own randomly offset melting threshold Tm + z·σ (z drawn from a standard normal distribution, σ = population heterogeneity), so the population denatures gradually. Averaged over the population this reproduces the textbook soluble-fraction curve as the cumulative distribution of that same Gaussian:
f(T) = 1/2 · [1 + erf((Tm − T) / (σ·√2))]
A drug that binds and thermodynamically stabilises its target protein raises that protein's apparent Tm — the classic melt-shift assay. The size of the shift follows a saturating (Langmuir) binding isotherm in ligand concentration [C]:
ΔTm(C) = ΔTm_max · C / (Kd + C)
An off-target / control protein that the drug does not bind shows no concentration-dependent shift — exactly what distinguishes a real target from background noise in a real TPP screen.
- Temperature slider / Run Melt Ramp — heat-challenges both populations, shown top-left and top-right as a schematic centrifuge tube: soluble copies float in the supernatant band, denaturing copies turn orange in place, and aggregated copies sink into the pellet band at the bottom and stay there.
- Concentration / Kd — set how much ligand is present and how tightly it binds; together they set the target's apparent ΔTm via the isotherm above, plotted live bottom-right with a marker at the current [C]. The control population ignores both sliders.
- Melt-curve chart (bottom-left) plots the exact soluble-fraction formula above for both populations against the current σ and marks live where the simulated population currently sits — the curve width is set entirely by the heterogeneity slider, not a fixed constant.
- Aggregation is irreversible — once a copy fully denatures it sinks into the pellet and stays there even if you cool back down, just as precipitated protein does not redissolve on ice.
Real-world relevance: this is the assay used to identify direct drug targets and off-target liabilities in intact cells without any prior knowledge of the mechanism — e.g. panobinostat and staurosporine target deconvolution, and large-scale kinase inhibitor profiling.