Real-time competitive kinetic analysis of interactions between low-molecular-weight ligands in solution and surface-immobilized receptors

Effect of multimerization of human and recombinant von Willebrand factor on platelet aggregation, binding to collagen and binding of coagulation factor VIII

The smallest circulating von Willebrand factor (vWF) molecule is a dimer composed of two identical subunits containing binding sites for heparin, collagen, platelet glycoproteins and coagulation factor VIII (FVIII). Interdimeric disulfide linking leads to multimers composed of up to 40 dimers. vWF serves as a carrier of FVIII and is required for normal interactions of platelets with the subendothelium of the injured vessel wall. Von Willebrand factor was purified from human plasma cryoprecipitate and fermentation supernatant of recombinant CHO cells by anion exchange chromatography. Heparin affinity chromatography was used to isolate vWF polymers of different degree of multimerization. Analysis of collagen binding and platelet aggregation revealed that these activities increase with increasing degree of multimerization of vWF. Binding of FVIII to vWF was studied by real-time biospecific interaction analysis and surface plasmon technology. The binding data showed that the binding of FVIII is independent of vWF multimerization. Using recombinant FVIII and recombinant vWF, real-time biospecific interaction analysis resulted in a potential stoichiometry of 2 to 2.5 vWF-subunits per bound FVIII molecule. The kinetic analysis of the vWF-FVIII interaction resulted in a binding rate constant of about 3 x 10(6) M-1 s-1 and an equilibrium dissociation constant of about 0.4 x 10(-9) M.

A TCR binds to antagonist ligands with lower affinities and faster dissociation rates than to agonists

T lymphocyte activation is mediated by the interaction of specific TCR with antigenic peptides bound to MHC molecules. Single amino acid substitutions are often capable of changing the effect of a peptide from stimulatory to antagonistic. Using surface plasmon resonance, we have analyzed the interaction between a complex consisting of variants of the MCC peptide bound to a mouse class II MHC (Ek) and a specific TCR. Using both an improved direct binding method as well as a novel inhibition assay, we show that the affinities of three different antagonist peptide-Ek complexes are approximately 10-50 times lower than that of the wildtype MCC-Ek complex for the TCR, largely due to an increased off-rate. These results suggest that the biological effects of peptide antagonists and partial agonists may be largely based on kinetic parameters.

Structure based design and characterization of peptides that inhibit IgE binding to its high-affinity receptor

We have designed synthetic peptide inhibitors of the interaction between IgE and its high affinity receptor, Fc epsilon RI. The structure of the second domain of CD2 was used as a modelling template for the second alpha-chain domain of Fc epsilon RI, the C-C' loop of which has been implicated in the interaction with IgE. An L-amino acid peptide and a retro-enantiomeric D-amino acid peptide were designed to mimic the conformation of the C-C' region. Both peptides were cyclized by disulphide bond formation between terminal cysteine residues, and show mirror image symmetry by circular dichroism analysis. The C-C' peptide mimics act as competitive inhibitors of IgE binding. The cyclic L- and retro D-peptides exhibited KDs of approximately 3 microM and 11 microM, respectively, for IgE. Further, the peptides inhibit IgE-mediated mast cell degranulation, an in vitro model of an allergic response.

Molecular interaction analysis in ligand design using mass transport, kinetic and thermodynamic methods

Ligand design in biotechnology is underpinned by the control of molecular affinity. Hence, measuring binding interactions is a key component in designing ligands for such uses as therapeutics, diagnostics, biomaterials and separation science. Mass transport, kinetic and thermodynamic methods have been used for macromolecular interaction analysis but also have potential applicability as direct methods for measuring small molecular interactions. They can enhance the ligand design process by providing the ability to choose ligands based on both their kinetic and thermodynamic binding properties.

Direct and competitive kinetic analysis of the interaction between human IgG1 and a one domain analogue of protein A

Direct and competitive kinetic analysis of the binding between a one domain analogue of protein A, and mutants thereof, to immobilised hIgG1 was compared using a biosensor system based on surface plasmon resonance detection. Rate constants determined from both assays were almost identical. The experiments demonstrate that competitive kinetic analysis can be used in combination with biosensor technology, and indicate that competitive kinetic analysis may extend the use of the technology to include low molecular weight analytes.