Supplementary Figure 7: Comparison of needle lengths of substrate-free (WT) and substrate-trapped (+pSptP3-GFP) needle complexes.
From: Structure of a pathogenic type 3 secretion system in action
(a,b) Substrate-trapped sucrose-gradient purified needle complexes displayed a broader distribution of needle lengths than substrate-free (WT) needle complexes. (The most frequent needle length for substrate-trapped NCs was 41.4 nm, and 29.9 nm for substrate-free NCs, respectively.) This suggested that the substrate-trapped sample was composed of a mixture of empty and substrate-trapped needle complexes and indicated that substrate-containing complexes indeed had longer needles. However, the molecular mechanism leading to this observation is unknown, but may be explained by an increased stability of the needle filament in the presence of substrate during the purification. (Box plot: the left and right border of the box represented the first and third quartiles, and the band inside the box the second quartile (median).
