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length and properly folded, and they can attach to the microscope slide in various orientations. The researchers have used the system to assay protein–protein interactions, to screen for enzyme substrates, and to study protein–small molecule interactions. In the small molecule experiments, even low-affinity interactions (Ka as low as 3.8 3 105/M) could be detected by coupling the ligands to BSA. This approach takes advantage of “avidity effects”, in which the ligand–target binding is enhanced because the BSA bears multiple copies of the ligand. (Science 2000, 289, 1760–1763)
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Everything’s coming up proteins. Even the relatively new DNA microarray technology is being co-opted for protein use, thanks to Gavin MacBeath and Stuart L. Schreiber at Harvard University. The result? Simultaneous functional analysis of >10,000 protein samples. One advantage of the new method is that it is compatible with commercially available instrumentation (which is currently used for making DNA microarrays). A high-precision robot deposits up to 10,800 protein spots (150to 200-µm diam) on a glass slide that has been coated with an aldehyde-containing silane reagent to capture proteins. Any unreacted aldehydes are later quenched with bovine serum albumin (BSA). By using an alternate protocol for preparing the slides, short peptides also can be analyzed. Detection is performed with a commercial fluorescence slide scanner. Additional advantages are that the proteins in the microarray are full-
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Protein microarrays
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D Detecting (A–C) three different protein–protein interactions separately or (E) together. In the (D) control, there is no binding because a critical helper molecule has been omitted. (Adapted with permission. Copyright 2000 American Association for the Advancement of Science.)
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Small molecule microarrays As further proof that microarrays are all the rage, Paul J. Hergenrother, Kristopher M. Depew, and Stuart L. Schreiber at Harvard University describe a method
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for screening arrays of alcohol-containing small molecules. In this technique, various alcoholcontaining small molecules are synthesized on and released from polystyrene beads. A commercial robotic microarrayer then deposits 300µm-diam spots of these solutions on a slide that has a chlorinated surface. The protein-binding partners of these small mole-
cules are fluorescently labeled and allowed to bind. The researchers note that the slides preferentially react with primary alcohol derivatives, even when the secondary or other derivatives are present in greater concentrations. In addition, they demonstrate that the technique can be used with split-pool synthesis, in which the beads are temporarily split into two groups during synthesis, tagged with different molecules, and recombined. (J. Am. Chem. Soc. 2000, 122, 7849–7850)
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Thionyl chloride-activated slide spotted with primary (top row), secondary, phenolic, and methyl ether derivatives of a ligand. The primary alcohol is favored. N O V E M B E R 1 , 2 0 0 0 / A N A LY T I C A L C H E M I S T R Y
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