J. Bacteriol., Sep 1996, 5320-5322, Vol 178, No. 17
Copyright © 1996, American Society for Microbiology

Demonstration of a folded monomeric form of porin PhoE of Escherichia coli in vivo

P Van Gelder and J Tommassen
Department of Molecular Cell Biology and Institute of Biomembranes, Utrecht University, The Netherlands.

The porins in the outer membranes of gram-negative bacteria are trimeric proteins. A folded monomeric form of the Escherichia coli porin PhoE, with a higher electrophoretic mobility than that of the denatured protein, has recently been detected in in vitro folding studies. To investigate the possible biological significance of the folded monomer, we 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 which the subunit interactions were weakened by a E-66-- >R substitution. Together, these results show that the folded monomer is not an in vitro folding artifact but an integral part of the native trimer.

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