Domain-level interactions
Find out which part of a multi-domain protein carries the binding.
Competitive and blocking assays compare truncations and mutants against the full-length protein.
competitive assays
Protein-protein interaction analysis: the kinetics your structure cannot show
A structure tells you what the complex looks like. It does not tell you how fast the partners find each other, how long they stay together, or whether your engineered variant still binds at all. The inQuiQ measures affinity (KD) and real-time kinetics (kon, koff) in solution, label-free, so your model gets functional evidence behind it.
Where structural biologists use label-free binding data
Label-free interaction analysis measures binding between unmodified molecules in real time. For structural biology it returns affinity, association and dissociation rates, and specificity in solution, so an atomic-resolution model can be tested against how the complex actually forms, how long it holds, and how it comes apart.
Predicted complexes
Test an AlphaFold or docking prediction at the bench.
A measured KD either supports the predicted interface or it does not.
KD validation
Engineered variants
Confirm a construct still binds the way its parent does.
Stabilised, truncated, and mutated constructs measured side by side before they enter a structural pipeline.
variant ranking
Triage before structure determination
Check that the complex forms before it takes up beam or microscope time.
Confirm binding and estimate how long the complex holds together, so structural work goes to samples that behave.
complex stability
Thermodynamics
Run the same interaction across a temperature series.
The temperature-controlled flow cell adds the thermodynamic layer to a binding measurement.
16 to 40 °C
Don't see your system?
Discuss your assay with one of our application specialists.
Talk to a specialist
Benefits of the inQuiQ in structural biology
01 / 04
One injection reads sixteen sensors.
Truncations, point mutants, and controls sit on the same chip, so a construct series moves as a batch rather than one measurement per surface.
*spotter necessary for 16-sensor immobilisation
30 µL minimumrun in series
four channels, sixteen sensors
Watch the complex form and come apart.
The rising phase gives kon, the falling phase gives koff, and together they give KD. Affinity runs from 10 pM to 10 mM, with steady-state fitting where dissociation is too fast for kinetics.
0.1 RU RMSkon, koff, KD
association, then dissociation
Measure in label-free conditions.
The analyte stay unmodified in solution, so the interaction is recorded as it behaves rather than as a tag or a label allows it to behave.
- No tag on either partner to shift affinity or sit across an interface
- Solution-phase binding, measured in real time
the same binding event
See which domain carries the binding.
Run the full-length protein against its truncations and point mutants, then use competitive and blocking assays to find the construct that keeps the affinity. The comparison localises an interaction without a new structure for every variant.
competitive assaysblocking assays
full length, or domain removed
How a binding run works
Every measurement follows the same steps, whatever the complex. One partner is immobilised on the sensor, the other flows past, and the instrument records the response in real time. An endpoint assay gives you one number. The inQuiQ gives you the full curve.
Immobilisation
One binding partner is attached to the sensor surface first.
Amine coupling or capture through a tag holds the protein in place. For a protein pair, the more stable or more readily produced partner usually is immobilised on the surface, and the other is injected. Ligand density is set high enough for a clear response without crowding the surface.
- amine coupling
- capture
- ligand density
Deactivation
Any activated site left unused is capped before the first sample arrives.
Without it the surface keeps reacting with whatever passes over, and non-specific binding shows up in the trace as signal that has nothing to do with the pair being measured. The response settles at a stable level, the immobilised amount.
- deactivation
- blocking
- non-specific binding
Association
The second partner flows across the surface and the response climbs.
Sample and running buffer are matched, since a small solvent mismatch shifts the bulk signal more than the binding does, and a reference channel subtracts what remains. Flow between 1 and 100 µL/min sets contact time, up to 300 µL/min for low-viscosity samples. The rising phase gives the on-rate, kon.
- solvent matching
- referencing
- kon
Dissociation
Buffer replaces the sample and the response falls as the complex comes apart.
The falling phase gives the off-rate, koff, and 1/koff gives how long the complex holds together. Fit a concentration series and you get kon, koff, and KD across 10 pM to 10 mM. Where dissociation is too fast to fit, the plateau of each injection gives steady-state affinity. Single-cycle kinetics runs the series uninterrupted when protein is scarce.
- complex lifetime
- koff
- KD
- steady state
- SCK
Regeneration
A regeneration buffer strips the bound partner and returns the sensor to baseline, ready for the next injection.
The immobilised partner stays in place, so every variant in a series meets the same surface. Inject, read, regenerate, repeat, unattended. Samples run one after another, and each injection is read by every sensor on the chip, so one sample can cover several constructs, mutants, or controls at once.
- regeneration
- automated cycling
- saveable sequences
Response (RU)
Time
What the inQuiQ does for structural biology
Six capabilities, one modular benchtop instrument, no labels anywhere in the workflow.
Many constructs, one small sample
Four flexibly addressable channels for improved assay freedom, with 16 sensors to read truncations, point mutants, and controls against one injected sample.
16 sensors (spotter required)
30 µL
Resolve weak and transient contacts
Baseline noise stays low enough that a small binding response is still readable.
0.1 RU RMS
Cover transient contacts through to stable core complexes
One affinity range spans the weak contacts at the edge of a model and the tight complexes at its centre, with steady-state fitting where kinetics run out.
10 pM to 10 mM
Localise the interaction
Competitive and blocking assays show which construct or domain carries the binding, on the same surface as the full-length protein.
competitive
blocking
Add thermodynamic detail
The temperature-controlled flow cell runs a full temperature series.
temp. control from 16 to 40 °C
Modular system for an increased throughput
Simply add an autosampler, and run a long variant or condition series unattended.
2×96 wells
2×384 wells
Application notes, publications, and data
From small molecule kinetics to antibody affinity, explore real binding data generated on inQuiQ. Each application note pairs a sensorgram with the affinity and kinetic values behind it.
Small Molecule Kinetics on inQuiQ
This white paper showcases the high sensitivity of ring resonator technology for measuring low-molecular-weight interactions, using Carbonic Anhydrase II (CAII) and two small-molecule binders as a model system.
APPLICATION NOTE
Antibody interaction analysis
Kinetic characterisation of antibodoes and whatnot
APPLICATION NOTE
Small molecule interactions
Ka and Kd for very tiny small biomolecules.
APPLICATION NOTE
Small molecule interactions
Ka and Kd for very tiny small biomolecules.
Start A conversation
Talk to an application scientist
Bring your system. We will tell you honestly whether label-free is the right method for it, and how the assay would be built.
Ready to see the inQuiQ in action?
Talk to an application scientist
Thirty minutes to discuss your assay design, before anyone mentions an instrument.
Download the inQuiQ brochure
Sensitivity, channel layout, footprint, and consumable formats in a couple of pages.
Delta Life Science
info@deltalifescience.nl
Send us an email, and we will get back to you as soon as possible.
info@deltalifescience.nl
Send us an email, and we will get back to you as soon as possible.
Questions researchers ask
Cryo-EM, X-ray crystallography, and NMR give structure. Label-free interaction analysis, ITC, mass photometry, and SEC-MALS give function and behaviour in solution. Label-free analysis with the inQuiQ adds affinity (KD) and kinetics (kon, koff), so you can show that a modelled interface produces measurable, specific binding under native conditions.
Express the predicted partners, measure their binding in solution, and compare the result with the prediction. A measured KD and a clean sensorgram support the model. Competitive assays against truncations or point mutants then test whether the predicted interface is the one that actually drives binding.
The inQuiQ runs from 30 µL of sample. Sensors are regenerable, so the same chip carries a series of variants, mutants, and controls rather than one measurement per surface. That matters for structural constructs that are slow to express or purify.
Yes, indirectly and reliably. Run the full-length protein on the inQuiQ and its truncations or domain constructs as separate binding experiments, then use competitive and blocking assays to see which construct carries the affinity. The comparison localises the interaction without needing a new structure for every variant.
Affinity (KD) says how tightly two molecules bind at equilibrium. Kinetics says how they get there: kon for how fast the complex forms, koff for how fast it falls apart. Two complexes can share a KD and behave differently, which is why structural work benefits from both.