Lattice models for the
peptidoglycan of long-bridged wild-type S. aureus (left) and its short-bridged FemA mutant (middle
and right). A 4 × 4 array of glycan chains perpendicular to the
plane of the paper is in gray, with the peptide stems in green and
the pentaglycyl bridges in red. Panels a through d for each model
are slices transverse to the glycan chain direction and separated
from one another by a single glycan repeat unit. The model on the
left has all nearest-neighbor stems parallel; that in the middle,
perpendicular; and that on the right, a mixed geometry. The expanded
insets on the far right identify structural components (arrows and
color highlights) for the mixed geometry of the FemA hybrid model.
The two red arrows (inset, upper right) identify strands that are
color highlighted in Figure 10. Alternate rows
of the mixed-geometry model have stems that are perpendicular to one
another. Thus, the stems of rows 1 and 3 are parallel, and those of
rows 2 and 4 are parallel. Counts for the central four strands of
the unit cells indicate that ideal cross-linking is 100% for the wild-type
lattice (each stem is a cross-link donor and acceptor) and 50% for
each of the two FemA models.