Receptor for bacteriophage lambda of Escherichia coli forms larger pores in black lipid membranes than the matrix protein (porin)

Abstract

The receptor for phage .lambda. in E. coli was isolated by cholate extraction and purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Protein bands corresponding to the monomer and the dimer were eluted from the gel and tested for their activity to inactivate phage .lambda. and to form pores in black lipid membranes. Only the dimer inactivated phage .lambda. but both the monomer and the dimer were active in forming pores. The pore characteristics were similar to those exhibited by the matrix protein (porin). In comparison, the .lambda. receptor showed a somewhat higher degree of cation specificity and its pore size was larger. Assuming that the thickness of the outer membrane is 7.5 nm and that the pore is an ideal hydrophilic channel, the pore diameter in vivo was estimated to be 1.6 nm for the .lambda. receptor and 1.2 nm for the matrix protein.