(a) X-ray structure of HPBP. The two globular domains are shown in pink and blue. They are hinged by an antiparallel two-stranded β-sheet acting as a hinge (in yellow), and form a deep cleft wherein a phosphate molecule is bound (red balls). The two disulfide bridges (C113–C158 and C306–C359) are shown by orange sticks. (b) Structural comparison of different known phosphate-SBPs: HPBP [Protein Data Bank (PDB) ID: 2v3q
] is shown in blue, PfluDING (PDB ID: 2q9t
) is shown in yellow, E. coli PstS protein (PDB ID: 1ixh
) is shown in red. The four protruding DING protein-specific loops are indicated by black arrows.