Figure 2: EB1-gold interacts with the outer surface of tubulin sheets and closed microtubule lattices.

(a,a ′) NPs of 6.5 nm average diameter at the end of a microtubule (Supplementary Table 2e). (b,b ′,c,c ′) NPs of 9.8 nm average diameter at the ends of microtubules with short (b, b ′) and long (c, c ′) sheet extensions (Supplementary Table 2g). The EB1-gold concentration was 94 nM and 22.5 nM with 6.5 nm and 9.8 nm NPs, respectively. Each panel comprises a projection along the Z direction that encompasses the microtubule and the NPs (a–c), Z projections of a few slices at the middle of the microtubule that highlight the shape of the tip (a ′, b ′, c ′), and cross-sections along the microtubule axis that reveal the organization of the NPs around the lattice (a1–4, b1–12, c1–8). Vertical bars on each side of views a–c indicate the sub-regions used to produce the corresponding cross-sections. The protofilament number, N, was determined on cross-sections of complete microtubule lattices (a5, b13, c9), and was confirmed using N-fold rotational averaging (a5′, b13′, c9′). Dotted circles surround pairs of NPs, and plain circles surround NP singlets. The histograms show the distribution of NPs from the tip up to the least visible portion of the microtubules in the tomograms. Data were binned every 50 nm. The horizontal bar above the histograms indicates the portion of the lattice organized as sheets, and the asterisks correspond to NPs in interaction with both the microtubule lattice and the air/water interfaces. These NPs were discarded from the statistical analysis. Scale bars, 20 nm, except in a5,5′, b13,13′, c9,9′ where they represent 10 nm.