PURIFICATION AND PARTIAL CHARACTERIZATION OF SYMBIONIN, AN APHID ENDOSYMBIONT-SPECIFIC PROTEIN

Symbionin, essentially the only protein produced by the pea aphid endosymbiont in vivo, was isolated and purified by ammonium sulfate precipitation, hydroxyapatite and DEAE-Sephacel column chromatography. While on two-dimensional gel electrophoresis symbionin is an acidic protein with a molecular mass of 63 kDa, an electron micrograph of the negatively-stained molecules suggested that native symbionin is a 14 subunit homo-oligomer of 63 kDa which is composed of two stacked rings of 7 subunits each. Symbionin was characterized by its high content of hydrophobic amino acids such as glycine, alanine, valine, isoleucine and leucine, and was low in phenolic amino acids. In this respect, symbionin is quite different from known storage proteins of insects. © 1990.