SPARK: a new peptidyl transferase activity assay.

The formation of peptide bonds is the central chemical reaction during protein synthesis and is catalyzed by the peptidyl transferase center residing in the large ribosomal subunit. This active site is composed of universally conserved rRNA nucleosides. The peptidyl transferase center is by far the most frequently used target site of natural antibiotics in the cell. Here we describe a novel, simple, and convenient method to assess peptide bond formation which we named SPARK. The basic principle of SPARK is the use of two reaction substrates that closely resemble the natural tRNA substrates (one is biotinylated and the other carries a tritium label) that become covalently connected during transpeptidation. Formation of this peptide bond then allows capture and direct quantification of the radiolabled product, now joined to the biotin group, using the scintillation proximity assay technology. Binding of the tritiated radioligand to streptavidin-coated beads causes the excitation of the bead-embedded scintillant, thus resulting in the detection of radioactivity. Since no product purification step is required, SPARK is amenable to simple automation, which makes it useful in high-throughput screens of natural or synthetic compound libraries in the search for novel antibiotics.