Figure 4.

NMR spectra and structures of the repeating units of WTA from Lmo serovar 4b WSLC1042. A, details of the ¹H-¹³C-HSQC and ¹H-³¹P-COSY spectra. For the major monomeric species the spectra suggest a phosphodiester linkage between Rbo C1′ and GlcNAc C4′ (cf. dotted vertical lines). A small HMBC insert exemplifies the assignment of glycosidic bonds. The HP-COSY spectrum also shows two correlations to lower intensity proton signals with chemical shifts of 4.15 and 4.25 ppm. The corresponding cross-peaks in the HSQC spectrum were assigned to the 4′ positions of 3′ O-acetylated GlcNAc in two minor variants of the monomeric subunit. The GlcNAc 3′ protons in these O-acetylated variants show a significant downfield shift to about 5.1 ppm. The biggest difference in chemical shift between the two minor sets of GlcNAc signals is observed for the 5′ position. This is in agreement with the expected lack of galactose in one of the variants. The asterisk indicates an artifact at the position of the ¹H resonance of the residual water signal. B, structures and atom designations of WTA monomeric units (cf. Table 2). A, Rbo (green); B, GlcNAc (purple); C, Glc (blue); D, Gal (red).