β-Galactosidase fused to the hydrophobic domain of cytochrome b₅ spontaneously associates with liposomes

Since liver microsomal cytochrome b₅ spontaneously associates with liposomes and membranes by means of its C-terminal hydrophobic domain (HP), chimeric proteins containing HP prepared by genetic fusion might also spontaneously associate with liposomes or cellular membranes. Synthetic DNA corresponding to the hydrophobic domain of cytochrome b₅ was enzymatically fused in-frame to cloned DNA corresponding to the C-terminus of the Escherichia coli enzyme, β-galactosidase. This protein, LacZ:HP, synthesized in E. coli and purified from a crude E. coli membrane extract, was shown to spontaneously associate with liposomes, as does cytochrome b₅. Association is rapid and stable in the presence of salt and high pH and the fusion protein behaves as an integral membrane protein. LacZ:HP can be readily and extensively purified from crude extracts by association with liposomes and this procedure may provide a convenient purification scheme for proteins not otherwise readily purified, for example polypeptides from cloned gene fragments to be used for antibody production. These hybrid proteins may represent a new potentially useful class of polypeptides capable of hydrophobic interactions with membranes.