Oligomeric structure of the neutral amino acid transporters KAAT1 and CAATCH1.
The highly homologous neutral amino acid transporters KAAT1 and CAATCH1, cloned from the midgut epithelium of the Manduca sexta larva, are members of the Na(+)/Cl(-)-dependent transporter family. Recent evidence indicates that transporters of this family form constitutive oligomers. CAATCH1 and KAAT1 give rise to specific kinds of current depending on the transported amino acid, cotransported ion, pH, and membrane voltage. Different substrates induce notably distinct transport-associated currents in the two proteins that represent useful tools in structural-functional studies. To determine whether KAAT1 and CAATCH1 form functional oligomers, we have constructed four concatameric proteins for electrophysiological analysis, consisting of one KAAT1 protein covalently linked to another KAAT1 (K-K concatamer) or to CAATCH1 (K-C concatamer) and vice versa (C-C concatamer and C-K concatamer), and eight constructs where the two transporters were linked to yellow or cyan fluorescent protein in the NH(2) or COOH terminus, to determine the oligomer formation and the relative distance between the different subunits by fluorescence resonance energy transfer (FRET) analysis. Heterologous expression of the concatenated constructs and coinjection of the original proteins in different proportions allowed us to compare the characteristics of the currents to those of the oocytes expressing only the wild-type proteins. All the constructs were fully active, and their electrophysiological behavior was consistent with the activity as monomeric proteins. However, the FRET studies indicate that these transporters form oligomers in agreement with the LeuT(Aa) atomic structure and confirm that the COOH termini of the adjacent subunits are closer than NH(2) termini.
Bossi
Elena
E
Laboratory of Cellular and Molecular Physiology, Department of Structural and Functional Biology, University of Insubria, Via Dunant 3, 21100 Varese, Italy. elena.bossi@uninsubria.it
Soragna
Andrea
A
Miszner
Andreea
A
Giovannardi
Stefano
S
Frangione
Valeria
V
Peres
Antonio
A
D026921:Amino Acid Transport Systems, Neutral / Q000235:genetics / Q000502:physiology*; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D003001:Cloning, Molecular; D005260:Female; D031541:Fluorescence Resonance Energy Transfer; D019476:Insect Proteins / Q000235:genetics / Q000502:physiology*; D008164:Luminescent Proteins / Q000235:genetics; D018402:Manduca; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D011485:Protein Binding; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000502:physiology; D014982:Xenopus laevis
D026921:Amino Acid Transport Systems, Neutral; C413023:CAATCH1 protein, insect; D002352:Carrier Proteins; D019476:Insect Proteins; C112249:KAAT1 protein, insect; D008164:Luminescent Proteins; D008565:Membrane Proteins; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins