Detecting ricin: sensitive luminescent assay for ricin A-chain ribosome depurination kinetics.
Ricin is a family member of the lethal ribosome-inactivating proteins (RIP) found in plants. Ricin toxin A-chain (RTA) from castor beans catalyzes the hydrolytic depurination of a single base from a GAGA tetraloop of eukaryotic rRNA to release a single adenine from the sarcin-ricin loop (SRL). Protein synthesis is inhibited by loss of the elongation factor binding site resulting in cell death. We report a sensitive coupled assay for the measurement of adenine released from ribosomes or small stem-loop RNAs by RTA catalysis. Adenine phosphoribosyl transferase (APRTase) and pyruvate orthophosphate dikinase (PPDK) convert adenine to ATP for quantitation by firefly luciferase. The resulting AMP is cycled to ATP to give sustained luminescence proportional to adenine concentration. Subpicomole adenine quantitation permits the action of RTA on eukaryotic ribosomes to be followed in continuous, high-throughput assays. Facile analysis of RIP catalytic activity will have applications in plant toxin detection, inhibitor screens, mechanistic analysis of depurinating agents on oligonucleotides and intact ribosomes, and in cancer immunochemotherapy. Kinetic analysis of the catalytic action of RTA on rabbit reticulocyte 80S ribosomes establishes a catalytic efficiency of 2.6 x 10(8) M(-1) s(-1), a diffusion limited reaction indicating catalytic perfection even with large reactants.
Sturm
Matthew B
MB
Department of Biochemistry, Albert Einstein College of Medicine of Yeshiva University, 1300 Morris Park Avenue, Bronx, New York 10461, USA.
Schramm
Vern L
VL
D000225:Adenine / Q000378:metabolism; D000249:Adenosine Monophosphate / Q000378:metabolism; D000818:Animals; D055029:Inverted Repeat Sequences; D007700:Kinetics; D049409:Luciferases, Firefly / Q000378:metabolism; D008163:Luminescent Measurements / Q000379:methods*; D009693:Nucleic Acid Hybridization; D011687:Purines / Q000378:metabolism*; D011772:Pyruvate, Orthophosphate Dikinase / Q000378:metabolism; D012313:RNA / Q000235:genetics / Q000378:metabolism; D012156:Reticulocytes / Q000378:metabolism; D054683:Ribosome Subunits, Large, Eukaryotic / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D012276:Ricin / Q000032:analysis* / Q000378:metabolism; D012680:Sensitivity and Specificity; D013997:Time Factors
D011687:Purines; D000249:Adenosine Monophosphate; D012313:RNA; D012276:Ricin; D049409:Luciferases, Firefly; D011772:Pyruvate, Orthophosphate Dikinase; D000225:Adenine