Fluorescence anisotropy capillary electrophoresis (FACE) and affinity probe capillary electrophoresis (APCE) with laser-induced fluorescence detection were evaluated for analysis of peptide-protein interactions with rapid binding kinetics. The Src homology 2 domain of protein SH2-Bbeta (SH2-Bbeta (525-670)) and a tyrosine-phosphorylated peptide corresponding to the binding sequence of JAK2 were used as a model system. For peptide labeled with fluorescein, the K(d) = 82 +/- 7 nM as measured by fluorescence anisotropy (FA). APCE assays had a limit of detection (LOD) of 100 nM or 12 amol injected for SH2-Bbeta (525-670). The separation time of 4 s, achieved using an electric field of 2860 V/cm on 7-cm-long capillaries, was on the same time scale as complex dissociation allowing K(d) (101 +/- 12 nM in good agreement with FA measurements) and dissociation rate (k(off) = 0.95 +/- 0.02 s(-)(1) corresponding to a half-life of 0.73 s) to be determined. This measurement represents a 30-fold higher rate of complex dissociation than what had previously been measurable by nonequilibrium CE analysis of equilibrium mixtures. Using FACE, the protein was detected with an LOD of 300 nM or 7.5 fmol injected. FACE was not used for determining K(d) or k(off); however, this method provided better separation resolution for multiple forms of the protein than APCE. Both methods were found suitable for analysis of cell lysate. These results demonstrate that FACE and APCE may be useful complements to existing techniques for exploring binding interactions with rapid kinetics.

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High-speed capillary electrophoresis (CE) was employed to detect binding and inhibition of SH2 domain proteins using fluorescently labeled phosphopeptides as affinity probes. Single SH2 protein-phosphopeptide complexes were detected and confirmed by competition and fluorescence anisotropy. The assay was then extended to a multiplexed system involving separation of three SH2 domain proteins: Src, SH2-Bbeta, and Fyn. The selectivity of the separation was improved by altering the charge of the peptide binding partners used, thus demonstrating a convenient way to control resolution for the multiplexed assay. The separation was completed within 6 s, allowing rapidly dissociating complexes to be detected. Two low molecular weight inhibitors were tested for inhibition selectivity and efficacy. One inhibitor interrupted binding interaction of all three proteins, while the other selectively inhibited Src only leaving SH2-Bbeta and Fyn complex barely affected. IC(50) of both selective and nonselective inhibitors were determined and compared for different proteins. The IC(50) of the nonselective inhibitor was 49 +/- 9, 323 +/- 42, and 228 +/- 19 microM (n = 3) for Src, SH2-Bbeta, and Fyn, respectively, indicating different efficacy of the nonselective inhibitor for different SH2 domain protein. It is concluded that high-speed CE has the potential for multiplexed screening of drugs that disrupt protein-protein interactions.

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Three HPLC columns packed with 3 microm, sub-2 microm, and 2.7 microm Fused-Core (superficially porous) particles were compared in separation performance using two natural product mixtures containing 15 structurally related components. The Ascentis Express C18 column packed with Fused-Core particles showed an 18% increase in column efficiency (theoretical plates), a 76% increase in plate number per meter, a 65% enhancement in separation speed and a 19% increase in back pressure compared to the Atlantis T3 C18 column packed with 3 microm particles. Column lot-to-lot variability for critical pairs in the natural product mixture was observed with both columns, with the Atlantis T3 column exhibiting a higher degree of variability. The Ascentis Express column was also compared with the Acquity BEH column packed with sub-2 microm particles. Although the peak efficiencies obtained by the Ascentis Express column were only about 74% of those obtained by the Acquity BEH column, the 50% lower back pressure and comparable separation speed allowed high-efficiency and high-speed separation to be performed using conventional HPLC instrumentation.