Isolation, characterization and cDNA cloning of a one-lobed transferrin from the ascidian Halocynthia roretzi

摘要

J.li111"ICl1JJl Wi1" I:)UliilCU Irom plasma Or me asclolan J1alocynthla roretzt by ion-exchange chromatography. The nolecular weight of the plasma transferrin was determined to be 52K by SDS-polyacrylamide gel electrophoresis and gel filtration. Ascidian plasma transferrin was found to bind one mole of iron ion per mole of protein. The reductive ~-pyridylethylated transferrin was subjected to Edman degradation analysis for determination of the N-terminal amino icid sequence, and it was also subjected to proteolytic fragmentation to yield peptide fragments, whose amino acid ,equences were determined by Edman degradation analysis. Using the above amino acid sequences, a cDNA clone [1880 base pairs) encoding a protein of 372 amino acids containing a signal peptide of 2J.amino acids was isolated from an H. roretzi hepatopancreas cDNA library. The reduced amino acid sequence contains the same sequences of the peptide fragments. A comparison of the amino acid sequence of ascidian transferrin with those of other members of the transferrin family revealed that the ascidian transferrin is composed of only the N-terminallobe of two-Iobed vertebrate transferrins. Thus, a one-Iobed transferrin is present in the ascidian H. roretzi.