Biomedical subjects

Tadeusz Janas

Publications and source records attributed to Tadeusz Janas.

3 recordsLinked to original sources

PubMed2006

Specific RNA binding to ordered phospholipid bilayers.

We have studied RNA binding to vesicles bounded by ordered and disordered phospholipid membranes. A positive correlation exists between bilayer order and RNA affinity. In particular, structure-dependent RNA binding appears for rafted (liquid-ordered) domains in sphingomyelin-cholesterol-1,2-dioleoyl-sn-glycero-3-phosphocholine vesicles. Binding to more highly ordered gel phase membranes is stronger, but much less RNA structure-dependent. All modes of RNA-membrane association seem to be electrostatic and headgroup directed. Fluorometry on 1,2-dimyristoyl-sn-glycero-3-phosphocholine liposomes indicates that bound RNA broadens the gel-fluid melting transition, and reduces lipid headgroup order, as detected via fluorometric measurement of intramembrane electric fields. RNA preference for rafted lipid was visualized and confirmed using multiple fluorophores that allow fluorescence and fluorescence resonance energy transfer microscopy on RNA molecules closely associated with ordered lipid patches within giant vesicles. Accordingly, both RNA structure and membrane order could modulate biological RNA-membrane interactions.

Binding Sites↗

PubMed2004

A membrane transporter for tryptophan composed of RNA.

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.

Amino Acid Transport Systems↗

PubMed2003

Visualization of membrane RNAs.

Using fluorescence microscopy, we show that previously isolated membrane-binding RNAs coat artificial phospholipid membranes relatively uniformly, except for a frequent tendency to concentrate at bends, membrane junctions, and other unusual sites. Membrane RNAs can also be visualized as single molecules or isolated complexes by atomic force microscopy (AFM) of free RNAs on mica. Finally, RNAs can be seen within membranes by AFM of RNA-liposomes immobilized on hydrophobic mica surfaces. Monomer RNAs appear globular, as expected for small RNAs. When mixed under conditions in which RNAs bind bilayers, RNA 9 and RNA 10 combine to yield about 80% of RNAs as mainly linear oligomers of approximately 2-8 molecules. Once inserted in membranes, the RNAs oligomerize further, yielding larger, irregular ropelike structures that prefer the edges of altered lipid patches. These properties can be interpreted in terms of RNA-RNA loop interactions, and the RNA effects on membranes can be explained in terms of an RNA preference for irregular lipid conformations. The RNA-bilayer system poses new opportunities for combining the properties of membranes and RNA in contemporary cells, and also in the ribocytes of an RNA world.

Binding Sites↗