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

Transferrin was isolated from plasma of the ascidian Halocynthia roretzi by ion-exchange chromatography. The molecular weight of the plasma transferri n was determined to be 52K by SDS polyacrylamide gel electrophoresis and ge l filtration. Ascidian plasma transferrin was found to bind one mole bf iro n ion per mole of protein. The reductive S-pyridylethylated transferrin was subjected to Edman degradation analysis for determination of the N-termina l amino acid sequence, and it was also subjected to proteolytic fragmentati on to yield peptide fragments, whose amino acid sequences were determined b y 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 21 amino acids was isolated from an H. roretzi hepatopanc reas cDNA library. The reduced amino acid sequence contains the same sequen ces of the peptide fragments. A comparison of the amino acid sequence of as cidian transferrin with those of other members of the transferrin family re vealed that the ascidian transferrin is composed of only the N-terminal lob e of two-lobed vertebrate transferrins. Thus, a one-lobed transferrin is pr esent in the ascidian H. roretzi. (C) 2001 Elsevier Science Inc. All rights reserved.