Figure 5.

Rotation of the three-bond $\beta$dGlc(1→6)$\beta$dGlcNAc linkages in GBSIII, Pn14 and the unbranched backbone PS. The $\varphi$, $\psi$ and $\omega$ angles describing the orientation of this linkage are labeled on the GBSIII fragment shown on the left. Contoured 2D (a) $\varphi$, $\psi$ PMF and (b) the $\varphi$, $\omega$ PMF surfaces for a $\beta$dGlc(1→6)$\beta$dGlcNAc disaccharide in the gas phase illustrate the range of motion possible for an unrestrained linkage. Contours are drawn at intervals of 1 kcal·mol${}^{-1}$ to a maximum of 12 kcal·mol${}^{-1}$ and ‘X’ markers indicate dihedral angle values from the six-sugar GBSIII epitope identified in the DP2-Fab crystal structure [13]. The range of motion actually explored by the 6RU oligosaccharides is demonstrated with time series scatter plots of the two central $\beta$dGlc(1→6)$\beta$dGlcNAc linkages in the 6RU strands superimposed on the PMFs as follows: (c) GBSIII $\varphi$, $\psi$; (d) GBSIII $\varphi$, $\omega$; (e) Pn14 $\varphi$, $\psi$; (f) Pn14 $\varphi$, $\omega$; (g) unbranched backbone $\varphi$, $\psi$; and (f) unbranched backbone $\varphi$, $\omega$.