DEMONSTRATION OF A FOLDED MONOMERIC FORM OF PORIN PHOE OF ESCHERICHIA-COLI IN-VIVO

The porins in the outer membranes of gram-negative bacteria are trimer ic proteins. A folded monomeric form of the Escherichia coli porin Pho E, with a higher electrophoretic mobility than that of the denatured p rotein, has recently been detected in in vitro folding studies. To inv estigate the possible biological significance of the folded monomer, w e attempted to detect this form in vivo. After pulse-labeling, folded monomers could be detected by immunoprecipitation. Furthermore, folded monomers were detected in a preparation of mutant PhoE porins, in whi ch the subunit interactions were weakened by a E-66-->R substitution. Together, these results show that the folded monomer is not an in vitr o folding artifact but an integral part of the native trimer.