Method of determining thermodynamic and kinetic parameters from measured off rates
A method for measuring a property of a binding interaction between a capture agent and a binding partner for the capture agent is provided. In certain embodiments, this method comprises: a) contacting a population of particles that are linked to a capture agent with a substrate comprising a binding partner to produce capture agent/binding partner complexes, wherein the population of particles comprises first particles that are bound to a single molecule of the capture agent and second particles that are bound to two molecules of the capture agent; b) applying a force to the bound support, wherein the force is in a direction that separates the particles from the support; and c) separately measuring the forces required to disassociate the first particles and the second particles from their respective complexes.
1. A method for measuring a property of a binding interaction between a capture agent and a binding partner for said capture agent, comprising:
a) contacting a population of particles that are linked to a capture agent with a substrate comprising a binding partner to produce capture agent/binding partner complexes, wherein said population of particles comprises first particles that are bound to a single molecule of said capture agent and second particles that are bound to two molecules of said capture agent;
b) applying a force to the particles, wherein said force is in a direction that separates said particles from said substrate;
c) separately measuring:
(i) the force required to disassociate the first particles from their respective complexes and
(ii) the force required to dissociate the second particles from their respective complexes;
d) calculating the off rates of said first particles and said second particles as a function of the applied force;
e) calculating the off rate for said first particles in the absence of applied force from the dependence of off rates on the applied force; and
f) calculating the on rates for binding said first particles and said second particles, using the respective off rates calculated in d) and e).
2. The method of claim 1 , wherein said force is a centrifugal force.
3. The method of claim 1 , wherein said force is a magnetic force.
4. The method of claim 1 , wherein said applying comprises increasing said force over a period of time, and observing the release of said particles from said support.
5. The method of claim 1 , wherein said particles are of a defined size and density.
6. The method of claim 1 , wherein said particles are made of borosilicate glass, polystyrene, silica, gold, melamine or iron oxide.
7. The method of claim 1 , wherein said particles are linked to said capture agent via a flexible tether.
8. The method of claim 1 , wherein said on rate is calculated by using the following formula:
k on =( k off −kB off ) 2 /kB off /c
wherein k off and kB off are the off rates of the first and second particles and c is the molar concentration of binding partner accessible to capture agents on a particle.
9. The method of claim 1 , wherein said capture agent is a protein or nucleic acid.
10. The method of claim 1 , wherein said binding partner is a protein or nucleic acid.
11. The method of claim 1 , wherein said substrate comprises a nucleic acid array.