INTESTINAL PEPTIDE TRANSPORTER OF THE ANTARCTIC HAEMOGLOBINLESS TELEOST CHIONODRACO HAMATUS

A member of peptide transporter family, well characterised in higher vertebrates, was found in the intestine of the Antarctic waters haemoglobinless teleost Chionodraco hamatus (PepT-Ice; Maffia et al. J. Exp. Biol. 206:705, 2003). PepT-Ice shares high similarity to the low-affinity mammalian PepT1, but also possesses cold-adapted features. To better clarify the molecular basis of PepT-Ice evolutive adaptation, we studied its structural characteristics and tissue distribution. The full-length nucleotide sequence encoding for PepT-Ice was obtained by RT-PCR and 5’-/3’-RACE. PepT-Ice cDNA was 2509 bp long, with an orf of 2232 bp encoding for a putative protein of 743 amino acids. Hydropathy analysis predicted at least 12 potential transmembrane domains (TMD) with a large extracellular loop between TMD IX and X. Six putative extracellular N-glycosilation sites and nine and three intracellular consensus regions for protein kinase C and protein kinase A were identified. PepT-Ice exhibited higher percentage of identity with mammalian PepT1 (59-61%) than PepT2 (48-50%). Also, highest identity (69%) was found with zebrafish PepT1. Phylogenetic analysis clustered PepT-Ice to the PepT1 branch of the phylogenetic tree, In PepT-Ice, the presence of such hydrophobic amino acids as Gly-599, Leu-160 and Gly-271 in substitution of two Glu and one Asp, respectively, could play a relevant role in adaptive mechanisms to cold, possibly reducing intramolecular interaction and increasing protein flexibility. Using PepT-Ice specific primers, 630 bp RT-PCR amplification products were detected in mRNA extracted from C. hamatus intestine, kidney, liver, gills, brain and heart. The molecular characterization of PepT-Ice has been achieved that might elucidate the low temperature adaptation mechanisms of membrane transporters and functional relationships among vertebrate peptide transporters.