FhuA barrel-cork hybrids are active transporters and receptors
Abstract
The crystal structure of Escherichia coli FhuA reveals a beta-barrel domain that is closed by a globular cork domain. It has been assumed that the proton motive force of the cytoplasmic membrane through the interaction of the TonB protein with the TonB box of the cork opens the FhuA channel. Yet, deletion of the cork results in an FhuA derivative, FhuADelta5-160, that still displays TonB-dependent substrate transport and phage receptor activity. To investigate this unexpected finding further, we constructed FhuADelta5-160 derivatives of FhuA proteins from Salmonella paratyphi B, Salmonella enterica serovar Typhimurium, and Pantoea agglomerans. The FhuADelta5-160 proteins inserted correctly into the outer membrane, and with the exception of the P. agglomerans protein, transported ferrichrome and albomycin. FhuA hybrids consisting of the beta-barrel of one strain and the cork of another strain were active and showed higher TonB-dependent ferrichrome transport rates than the corkless derivatives. Exceptions were the E. coli beta-barrel/Salmonella serovar Typhimurium cork hybrid protein and the Salmonella serovar Typhimurium beta-barrel/P. agglomerans cork hybrid protein, both of which were less active than the beta-barrels alone. ...Continue Reading
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