TOPOLOGICAL ANALYSES OF THE L-FUCOSE-H-COLI( SYMPORT PROTEIN, FUCP, FROM ESCHERICHIA)

The transport of L-fucose into Escherichia coli is mediated by the L-f ucose-H+ symport protein (FucP). The fucP gene has been sequenced and encodes a hydrophobic protein that contains 438 amino acid residues, w ith a predicted M(r) of 47773. The hydropathic profile of FucP indicat es 10 to 12 hydrophobic regions that could span the membrane as alpha- helices. A 12-helix model with the N- and C-termini located in the cyt oplasm was derived from the hydropathic profile and from application o f the 'positive inside' rule. This model was tested using beta-lactama se fusion technology. Analyses of 62 different FucP-beta-lactamase fus ions suggested that the FucP protein crosses the cytoplasmic membrane of E. coli 12 times, with the N- and C-termini in the cytoplasm. From measurements of [C-14]-L-fucose uptake, it was deduced that the last p utative transmembrane region must be complete for transport activity t o be retained and that the four C-terminal residues were unnecessary f or transport activity. Fourier transform analyses show that all the pr edicted helices contain a periodicity that enables hydrophobic/hydroph ilic faces to be identified; these were particularly evident in putati ve helices 1, 3, 4, 5, 6, 10 and 11.