ISOLATION AND CHARACTERIZATION OF MOSQUITO FERRITIN AND CLONING OF A CDNA THAT ENCODES ONE SUBUNIT

Ferritin, an iron storage protein, was isolated from larvae and pupae of Aedes aegypti grown in an iron-rich medium. Mosquito ferritin is a high molecular weight protein composed of several different, relativel y small, subunits. Subunits of molecular mass 24, 26, and 28 kDa are e qually abundant, while that of 30 kDa is present only in small amounts . The N-terminal sequence of the 24 and 26 kDa subunits are identical for the first 30 amino acids, while that of the 28 kDa subunit differs . Studies using antiserum raised against a subunit mixture showed that the ferritin subunits were present in larvae, pupae, and adult female s, and were increased in animals exposed to excess iron. The antiserum also was used to screen a cDNA library from unfed adult female mosqui toes. Nine clones were obtained that differed only in a 27 bp insertio n in the 3' end. Rapid amplification of cDNA ends (RACE) was used to o btain the complete protein coding sequence. A putative iron-responsive element (IRE) is present in the 5'-untranslated region. The deduced a mino acid sequence shows a typical leader sequence, consistent with th e fact that most insect ferritins are secreted, rather than cytoplasmi c proteins. The sequence encodes a mature polypeptide of 20,566 molecu lar weight, smaller than the estimated size of any of the subunits. Ho wever, the sequence exactly matches the N-terminal sequences of the 24 and 26 kDa subunits as determined by Edman degradation. Of the known ferritin sequences, that of the mosquito is most similar to that of so matic cells of a snail. (C) 1995 Wiley-Liss, Inc.