A novel eukaryotic Na+ methionine selective symporter is essential for mosquito development

AeNAT5 (NCBI, ABZ81822), an orphan member of the insect-specific Nutrient Amino acid Transporter subfamily of SoLute Carrier family 6 (NAT-SLC6) and the first representative of a novel eukaryotic methionine-selective transport system (M), was cloned from cDNA of the vector mosquito, Aedes aegypti. It has orphan orthologs throughout several mosquito genomes, but not in Drosophila or outside Diptera. It shows the highest apparent affinity to L-Met (K(0.5) = 0.021 mM) and its metabolites Homocysteine and Cysteine (K(0.5) = 0.89 and 2.16 mM), but weakly interact with other substrates. It has a Na(+) - coupled mechanism (K(0.5) Na(+) ∼ 46 mM) with 1AA:1Na(+) stoichiometry that maintains ∼60% activity in Cl(-) - free media. In situ hybridization showed accumof AeNAT5 transcript in the absorptive and secretory epithelia, as well as in specific peripheral neurons and the central ganglia of mosquito larvae. The labeling pattern is distinct from that of the previously characterized AeNAT1. RNAi of AeNAT5 increases larval mortality during ecdysis and dramatically suppresses adult emergence. Our results showed that in addition to previously characterized broad spectra and aromatic amino acid selective transport systems, the mosquito NAT-SLC6 subfamily evolved a unique mechanism for selective absorption of sulfur-containing substrates. We demonstrated specific patterns of alimentary and neuronal transcription of AeNAT5 in mosquito larvae that is collateral with the indispensable function of this transporter in mosquito development.