DETERGENT-INDUCED FOLDING OF THE OUTER-MEMBRANE PROTEIN PHOE, A PORE PROTEIN-INDUCED BY PHOSPHATE LIMITATION

The folding of the in vitro synthesized outer-membrane protein PhoE, a protein induced by phosphate limitation, has previously been studied using immunoprecipitation experiments with monoclonal antibodies that recognize conformational epitopes [De Cock, H., Hendriks, R., de Vrije , T. and Tommassen, J. (1990) J. Biol. Chem. 265, 4646-4651]. A folded monomer of the protein was detected in this way, while the addition o f outer membranes was required to induce trimerization. In this study, we demonstrate that the folding of the in vitro synthesized PhoE prot ein did not occur spontaneously, but was dependent on the detergent th at was present in the immunoprecipitation buffer. A remarkable specifi city of phenyl-containing detergents on the efficient in vitro folding of PhoE molecules was observed. Furthermore, trimerization was detect ed in the absence of outer membranes when such detergents were present . However, the rate of trimerization was increased by the addition of crude cell envelopes containing outer membranes. The outer membranes p robably enhanced trimerization by concentrating the folded PhoE molecu les.