Figure 6.

Comparison of LpoA domain structures from different crystal forms. A, N domain twists and flexes. Overlay of the N domains of chain B of LpoA-N (cyan), LpoA^Ort (magenta), and LpoA^Mon (orange) on that of chain A of LpoA-N (gray), based on least-squares fittings of their subdomain 1 (residues 33–149, left half of the figure). Rotations of the first three N-domain structures by about 4.7, 4.0, and 4.3°, respectively, around the correspondingly colored rotation axes yielded the best superpositions of their subdomains 2 (residues 150–248, right half of the figure) onto that of chain A of LpoA-N. This rotation axis in LpoA^Ort (magenta) passes through residue 148 and is approximately parallel to H5, whereas that in LpoA^Mon (orange) is almost parallel to H8. The rotation axis for chain B of LpoA-N (cyan) runs through the center of subdomain 2 and is almost perpendicular to the LpoA^Mon axis. B, hinge bending in C domain. Shown is an overlay of the C domain of LpoA^Mon2 chain B (green) on that of LpoA^Mon (orange), after fitting their N lobes (residues 360–488 and 560–573) to each other. The C lobe of the LpoA^Mon2 chain B C domain was observed to be rotated, here by 12.1° around the green axis, with respect to the LpoA^Mon C lobe. Supplemental Fig. S2 shows two other C-domain comparisons. C, the consequence of the two lobes of the C domain spreading apart in B is that the LpoA^Mon2 chain B (bottom; green solvent contact surface) has a more direct pathway (black arrow) to the electronegative region on top of the C domain (red arrow; also see Fig. 4E). In contrast, in the LpoA^Mon (top, orange) C-domain structure, access to the electronegative region is blocked. This may affect the site accessibility to a bound polypeptide or PG strand.