PREDICTED TOPOLOGY OF THE N-TERMINAL DOMAIN OF THE HYDROPHILIC SUBUNIT OF THE MANNOSE TRANSPORTER OF ESCHERICHIA-COLI

A folding topology for the homodimeric N-terminal domain (IIA, 2 x 14 kDa) of the hydrophilic subunit (IIAB(man)) of the mannose transporter of E. coli is proposed. The prediction is based on (i) tertiary struc ture prediction methods, and (ii) functional properties of site-direct ed mutants in correlation with NMR-derived alpha/beta secondary struct ure data. The 3D structure profile suggested that the overall fold of IIA is similar to that of the unrelated protein, flavodoxin, which is an open-stranded parallel beta-sheet with a strand order of 5 4 3 1 2. The 3D model of IIA, constructed using the known atomic structure of flavodoxin, is consistent with the results from site-directed mutagene sis. Recently NMR results confirmed the open parallel beta-sheet with a strand order of 4 3 1 2 (residues 1-120) of our model whereas beta-s trand 5 (residues 127-130) was shown to be antiparallel to beta-strand 4. The correctly predicted fold includes 90% of the monomeric subunit sequence and contains all functional sites of the IIA domain.