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Characterization of a bioengineered chimeric Na+-nucleoside transporter
1Department of Biopharmaceutical Sciences, University of California, San Francisco, San Francisco, California, USA.
Molecular Pharmacology
|February 3, 1999
Summary
A new chimeric nucleoside transporter, T8, accepts both purine and pyrimidine nucleosides, similar to N3. However, its Na+/nucleoside transport stoichiometry matches N1 and N2, differing from N3.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Na+-dependent nucleoside transporters (N1, N2, N3) regulate intracellular purine and pyrimidine nucleoside uptake.
- N1 is purine-selective, N2 is pyrimidine-selective, and N3 exhibits broad selectivity.
- A chimeric transporter, T8, was engineered from rat N1 and N2 transporters.
Purpose of the Study:
- To characterize the substrate profile, transport mechanisms, and Na+-coupling stoichiometry of the chimeric transporter T8.
- To compare T8's characteristics with those of wild-type N1, N2, and N3 transporters.
Main Methods:
- Expression of T8 in Xenopus laevis oocytes.
- Measurement of Na+-dependent uptake of radiolabeled purine and pyrimidine nucleosides.
- Analysis of competitive inhibition by various nucleoside analogs.
- Determination of Na+/nucleoside stoichiometric ratios.
Main Results:
- T8 demonstrated enhanced uptake of both purine and pyrimidine nucleosides, indicating broad substrate acceptance.
- Competitive inhibition studies revealed a shared binding site for purine and pyrimidine nucleosides in T8.
- T8's substrate profile closely resembled N3, not a combination of N1 and N2.
- The Na+/nucleoside stoichiometric ratio for T8 was determined to be 1:1, consistent with N1 and N2, but distinct from N3.
Conclusions:
- The chimeric transporter T8 exhibits a substrate selectivity profile similar to the broadly selective N3 transporter.
- Despite its substrate similarity to N3, T8's Na+-coupling stoichiometry aligns with the purine-selective N1 and pyrimidine-selective N2 transporters.
- These findings highlight the complex interplay between transporter structure and function in determining substrate specificity and transport mechanism.