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A membrane transporter for tryptophan composed of RNA
A membrane transporter for tryptophan composed of RNA.
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We have incorporated an RNA binding site for the biological amino acid tryptophan within an RNA complex with affinity for phospholipid bilayer membranes. The resulting RNA (9:10Trp) creates a selective route through the bilayer for the amino acid. Binding and enhanced tryptophan permeability are nonlinear in RNA concentration, suggesting that RNA aggregation is required for both. Tryptophan permeability saturates with increased concentration, though at approximately 1000-fold greater level than when binding a free aptamer. The RNA (9:10Trp) complex, bound at a mean of two per liposome, halves the activation energy for tryptophan transport (to 46 kJ/mole), specifically increasing tryptophan entry to a maximal velocity of 0.5 sec(-1) per liposome with little or no accompanying increase in general permeability. Individual RNAs turn over tens of thousands of times at high tryptophan concentration. Thus, a specific passive membrane transporter whose properties overlap those of single-molecule transporter proteins, can be made of RNA alone. Permeability changes probably rely on disturbances in lipid conformation as well as on an advantageous low free energy position for tryptophan at the membrane. Other RNA activities may yield other RNA-membrane nanosystems via this route.
Janas T, Janas T, Yarus M
RNA (New York, N.Y.)
2004-10-01 00:00
10
10
1541-9
Amino Acid Transport Systems,Base Sequence,Binding Sites,Biological Transport, Active,Kinetics,Lipid Bilayers,Liposomes,Nucleic Acid Conformation,Permeability,Phospholipids,RNA,Thermodynamics,Tryptophan,Amino Acid Transport Systems,Lipid Bilayers,Liposomes,Phospholipids,RNA,Tryptophan
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA
RNA
NIGMS GM 30881
1355-8382
10.1261/rna.7112704
10/10/1541
1386
True
15383677
