New strategy for the conformational analysis of carbohydrates based on NOEand C-13 NMR coupling constants. Application to the flexible polysaccharide of Streptococcus mitis J22
M. Martin-pastor et Ca. Bush, New strategy for the conformational analysis of carbohydrates based on NOEand C-13 NMR coupling constants. Application to the flexible polysaccharide of Streptococcus mitis J22, BIOCHEM, 38(25), 1999, pp. 8045-8055
For complex oligosaccharides, which are relatively rigid with modest excurs
ions from a single minimum energy conformation, it is straightforward to bu
ild conformational models from NOE data. Other oligosaccharides are more fl
exible with transitions between distinct minima separated by substantial en
ergy barriers. We show that modeling based on scalar coupling data is super
ior to NOE-based modeling for the latter case. Long range C-13-C-13 and C-1
3-H-1 coupling constants measured for the heptasaccharide repeating subunit
of the cell wall polysaccharide from Streptococcus mitis J22 are correlate
d with individual glycosidic dihedral angles, effectively uncoupling the de
grees of freedom of the oligosaccharide and allowing a search for combinati
ons of dihedral angles which are energetically reasonable, i.e., with no ba
d van der Waals contacts, and which can be combined to satisfy all the meas
ured J values. Allowed values of the individual angles can then be combined
to search for overall oligosaccharide conformations which contribute to th
e ensemble. We show that while the polysaccharide from S. mitis J22 is flex
ible, requiring multiple conformations, most of the flexibility is localize
d to a few bonds and only a rather small number of conformations is require
d to reproduce the experimental NOE and scalar coupling data.