Conformational Analysis of β-1,2-Linked Mannobiose to Mannoheptaose, Specific Antigen of Pathogenic Yeast Candida albicans

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Candida albicans contains characteristic β-1,2-linked oligomannosyl moieties in the cell wall mannan. Reduction of the reducing termini of these oligosaccharides by NaBH4 causes a significant downfield shift in the NMR signals for the second and third mannose units and upfield shift of the fourth mannose unit. To show the correlation between the shift in the NMR signals and the conformations of the β-1,2-linked mannooligosaccharides, we performed molecular mechanics calculations. Six energy minima of the β-1,2-linked mannobiose were found in the relaxed map computed using the AMBER force field. Five of the six energy minima could also be generated by a simulated annealing from a 900 K molecular dynamics. Similarly, the solution conformation of the β-1,2-linked mannotriose to mannoheptaose was identified by the high temperature-simulated annealing. In the mannotetraose, the nonreducing terminal mannose unit was located near the reducing terminal one and formed a folded conformation. This result suggests that a mannose unit affects the H-1 chemical shifts of not only the second mannose unit, but also the third and fourth mannose units.