Molecular chaperon produced by an intracellular symbiont.

Symbionin, that is selectively produced by an intracellular symbiont harbored by the aphid bacteriocyte, is structurally homologous to the Escherichia coli groEL protein, a heat shock protein functioning as a molecular chaperon. It was shown that symbionin has ATPase activity and, in the presence of Mg-ATP, is converted into lower molecular mass species. Like the groEL protein, symbionin was able to reconstitute dimeric ribulose 1,5-bisphosphate carboxylase/oxygenase holoenzyme from its unfolded subunits in vitro, suggesting that this protein functions as a molecular chaperon in the endosymbiont. The groES-homologous protein did exist in the endosymbiont, but its amount was small relative to that of symbionin.