Predicted topology of the N‐terminal domain of the hydrophilic subunit of the mannose transporter of Escherichia coli

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Abstract
A folding topology for the homodimeric N‐terminal domain (IIA, 2 × 14 kDa) of the hydrophilic subunit (IIABman) of the mannose transporter of E. coli is proposed. The prediction is based on (i) tertiary structure prediction methods, and (ii) functional properties of site‐directed mutants in correlation with NMR‐derived α/β secondary structure 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 β‐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 mutagenesis. Recently NMR results confirmed the open parallel β‐sheet with a strand order of 4 3 12 (residues 1‐120) of our model whereas β‐strand 5 (residues 127–130) was shown to be antiparallel to β‐strand 4. The correctly predicted fold includes 90% of the monomeric subunit sequence and contains all functional sites of the IIA domain.