title: The D-amino acid transport by the invertebrate SLC6 transporters KAAT1 and CAATCH1 from Manduca sexta.
abstract: The ability of the SLC6 family members, the insect neutral amino acid cotransporter KAAT1(K(+)-coupled amino acid transporter 1) and its homologous CAATCH1(cation anion activated amino acid transporter/channel), to transport D-amino acids has been investigated through heterologous expression in Xenopus laevis oocytes and electrophysiological techniques. In the presence of D-isomers of leucine, serine, and proline, the msKAAT1 generates inward, transport-associated, currents with variable relative potencies, depending on the driving ion Na(+) or K(+). Higher concentrations of D-leucine (≥1 mmol/L) give rise to an anomalous response that suggests the existence of a second binding site with inhibitory action on the transport process. msCAATCH1 is also able to transport the D-amino acids tested, including D-leucine, whereas L-leucine acts as a blocker. A similar behavior is exhibited by the KAAT1 mutant S308T, confirming the relevance of the residue in this position in L-leucine binding and the different interaction of D-leucine with residues involved in transport mechanism. D-leucine and D-serine on various vertebrate orthologs B(0)AT1 (SLC6A19) elicited only a very small current and singular behavior was not observed, indicating that it is specific of the insect neutral amino acid transporters. These findings highlight the relevance of D-amino acid absorption in the insect nutrition and metabolism and may provide new evidences in the molecular transport mechanism of SLC6 family.
authors.affiliation: Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Vollero
authors.affiliation: Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy.
authors.forename: Francesca G
authors.initials: FG
authors.lastname: Imperiali
authors.affiliation: Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy.
authors.forename: Raffaella
authors.initials: R
authors.lastname: Cinquetti
authors.affiliation: Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Margheritis
authors.affiliation: Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Peres
authors.affiliation: Department of Biotechnology and Life Sciences, University of Insubria, Varese, Italy Interuniversity Center "The ProteinFactory", Politecnico di Milano, ICRM-CNR Milano and Università dell'Insubria, Milan, Italy elena.bossi@uninsubria.it.
authors.forename: Elena
authors.initials: E
authors.lastname: Bossi
mesh_terms: D026921:Amino Acid Transport Systems, Neutral / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D019476:Insect Proteins / Q000378:metabolism*; D007536:Isomerism; D018402:Manduca / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D021381:Protein Transport / Q000502:physiology*
chemical_list: D026921:Amino Acid Transport Systems, Neutral; D000596:Amino Acids; C413023:CAATCH1 protein, insect; D002352:Carrier Proteins; D019476:Insect Proteins; C112249:KAAT1 protein, insect; D008565:Membrane Proteins
keywords: D‐amino acids; SLC6; Xenopus oocytes; voltage clamp