Molecular features of the L-type amino acid transporter 2 determine different import and export profiles for thyroid hormones and amino acids

Mol Cell Endocrinol. 2017 Mar 5;443:163-174. doi: 10.1016/j.mce.2017.01.024. Epub 2017 Jan 18.

Abstract

The L-type amino acid transporter 2 (LAT2) imports amino acids (AA) and also certain thyroid hormones (TH), e.g. 3,3'-T2 and T3, but not rT3 and T4. We utilized LAT2 mutations (Y130A, N133S, F242W) that increase 3,3'-T2 import and focus here on import and export capacity for AA, T4, T3, BCH and derivatives thereof to delineate molecular features. Transport studies and analysis of competitive inhibition of import by radiolabelled TH and AA were performed in Xenopus laevis oocytes. Only Y130A, a pocket widening mutation, enabled import for T4 and increased it for T3. Mutant F242W showed increased 3,3'-T2 import but no import rates for other TH derivatives. No export was detected for any TH by LAT2-wild type (WT). Mutations Y130A and N133S enabled only the export of 3,3'-T2, while N133S also increased AA export. Thus, distinct molecular LAT2-features determine bidirectional AA transport but only an unidirectional 3,3'-T2 and T3 import.

Keywords: Competitive inhibition studies; Homology model; Molecular import and export; Site-directed mutagenesis; Thyroid hormone transport; Xenopus laevis oocytes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Transport System y+ / genetics*
  • Amino Acid Transport System y+ / metabolism*
  • Amino Acids / metabolism*
  • Amino Acids, Cyclic / pharmacology
  • Animals
  • Biological Transport / drug effects
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Diiodothyronines / metabolism
  • Fusion Regulatory Protein 1, Light Chains / genetics*
  • Fusion Regulatory Protein 1, Light Chains / metabolism*
  • Fusion Regulatory Protein-1 / metabolism
  • Green Fluorescent Proteins / metabolism
  • HEK293 Cells
  • Humans
  • Iodine / metabolism
  • Kinetics
  • Mice
  • Models, Biological
  • Models, Molecular
  • Mutant Proteins / metabolism
  • Mutation / genetics
  • Oocytes / drug effects
  • Oocytes / metabolism
  • Protein Multimerization
  • Substrate Specificity / drug effects
  • Thyroid Hormones / metabolism*
  • Xenopus laevis / metabolism

Substances

  • Amino Acid Transport System y+
  • Amino Acids
  • Amino Acids, Cyclic
  • Diiodothyronines
  • Fusion Regulatory Protein 1, Light Chains
  • Fusion Regulatory Protein-1
  • Mutant Proteins
  • SLC7A8 protein, mouse
  • Thyroid Hormones
  • Green Fluorescent Proteins
  • 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid
  • 3,3'-diiodothyronine
  • Iodine