Figure 1: Preliminary map of the Shigella flexneri needle architecture.

(a) Anchor point identification in the absence of previous structural knowledge. Proximity anchors are identified by at least two unambiguous (corresponding to well-resolved and readily assigned cross-peaks) or abundant (≥4) contacts in spectra of [1-13C]-glucose- and [2-13C]-glucose-labelled MxiH needles (gray lines, line thickness proportional to the number of contacts). (b) Strategy for assignment of ssNMR constraints arising from distinct intra-molecular and inter-molecular interfaces in helical assemblies. Pink lines indicate interface assignments of a given contact that are inconsistent with the axial displacement among symmetry-related subunits, and green lines the correct interface assignments.