Identification of a novel sugar-H⁺ symport protein, FucP, for transport of L-fucose into Escherichia coli.

L-Fucose (6-deoxy-L-galactose) is used as sole carbon source by many microorganisms, and its transport into Escherichia cell is mediated by an L-fucose-H+ symport activity. In order to determine the nature of a putative transporter encoded by the E. coli fucP gene and identify its protein product it was cloned downstream of the inducible T7 RNA polymerase and lambda OLPL promoters. Induction of the T7 promoter resulted in the expression of [C-14]-L-fucose uptake activity and the concomitant expression of a [S-35]-Met-labelled 32 kDa protein at levels too low for detection by staining with Coomassie brilliant blue or for protein sequencing. Induction of the lambda OLPL promoter caused the appearance of L-fucose-H+ symport activity and of a Coomassie brilliant blue-stained 32 kDa membrane protein expressed at high levels sufficient for Identification as FucP by N-terminal protein sequencing. The FucP protein is, therefore, a sugar-H+ symporter different in amino acid sequence from any other known transporter. These and other results illustrate the general unpredictability of cloning strategies for attempting the amplified expression of membrane transport proteins.