Structure of a cell wall mannan from the pathogenic yeast, Candida catenulata: assignment of 1H nuclear magnetic resonance chemical shifts of the inner alpha-1,6-linked mannose residues substituted by a side chain

We performed an enzyme-linked immunosorbent assay of the cell wall mannan purified from the pathogenic yeast, Candida catenulata, using antisera to factors of the genus Candida. The results suggest that mannan possesses a linear backbone consisting of alpha-1, 6-linked mannose residues and side chains possessing nonreducing terminal alpha-1,2- and alpha-1,3-linked mannose residues. The chemical structure of the mannan was analyzed by two-dimensional homonuclear Hartmann-Hahn and two-dimensional nuclear Overhauser enhancement and exchange spectroscopy. The sequential assignments of the cross-peaks caused by J-coupling and the nuclear Overhauser effect from these terminal mannose residues demonstrate that the H1 signal of an inner alpha-1,6-linked mannose residue substituted by an alpha-oligomannosyl side chain or a single mannose through the C-2 position in an alpha-anomer configuration undergoes a significant downfield shift (delta delta = 0.16 or 0.19 ppm, respectively) compared with that of unsubstituted residues. We therefore propose the exact overall structure of the antigenic mannan obtained from C. catenulata. The assignment data in the present study are useful for the determination of the exact overall structure of various yeast mannans using the two-dimensional nuclear magnetic resonance analysis without the need for harsh procedures.